[linux-2.6-omap-h63xx.git] / fs / ocfs2 / dlm / dlmmaster.c

/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * dlmmod.c
 *
 * standalone DLM module
 *
 * Copyright (C) 2004 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 *
 */


#include <linux/module.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/utsname.h>
#include <linux/init.h>
#include <linux/sysctl.h>
#include <linux/random.h>
#include <linux/blkdev.h>
#include <linux/socket.h>
#include <linux/inet.h>
#include <linux/spinlock.h>
#include <linux/delay.h>


#include "cluster/heartbeat.h"
#include "cluster/nodemanager.h"
#include "cluster/tcp.h"

#include "dlmapi.h"
#include "dlmcommon.h"
#include "dlmdebug.h"
#include "dlmdomain.h"

#define MLOG_MASK_PREFIX (ML_DLM|ML_DLM_MASTER)
#include "cluster/masklog.h"

enum dlm_mle_type {
        DLM_MLE_BLOCK,
        DLM_MLE_MASTER,
        DLM_MLE_MIGRATION
};

struct dlm_lock_name
{
        u8 len;
        u8 name[DLM_LOCKID_NAME_MAX];
};

struct dlm_master_list_entry
{
        struct list_head list;
        struct list_head hb_events;
        struct dlm_ctxt *dlm;
        spinlock_t spinlock;
        wait_queue_head_t wq;
        atomic_t woken;
        struct kref mle_refs;
        int inuse;
        unsigned long maybe_map[BITS_TO_LONGS(O2NM_MAX_NODES)];
        unsigned long vote_map[BITS_TO_LONGS(O2NM_MAX_NODES)];
        unsigned long response_map[BITS_TO_LONGS(O2NM_MAX_NODES)];
        unsigned long node_map[BITS_TO_LONGS(O2NM_MAX_NODES)];
        u8 master;
        u8 new_master;
        enum dlm_mle_type type;
        struct o2hb_callback_func mle_hb_up;
        struct o2hb_callback_func mle_hb_down;
        union {
                struct dlm_lock_resource *res;
                struct dlm_lock_name name;
        } u;
};

static void dlm_mle_node_down(struct dlm_ctxt *dlm,
                              struct dlm_master_list_entry *mle,
                              struct o2nm_node *node,
                              int idx);
static void dlm_mle_node_up(struct dlm_ctxt *dlm,
                            struct dlm_master_list_entry *mle,
                            struct o2nm_node *node,
                            int idx);

static void dlm_assert_master_worker(struct dlm_work_item *item, void *data);
static int dlm_do_assert_master(struct dlm_ctxt *dlm, const char *lockname,
                                unsigned int namelen, void *nodemap,
                                u32 flags);

static inline int dlm_mle_equal(struct dlm_ctxt *dlm,
                                struct dlm_master_list_entry *mle,
                                const char *name,
                                unsigned int namelen)
{
        struct dlm_lock_resource *res;

        if (dlm != mle->dlm)
                return 0;

        if (mle->type == DLM_MLE_BLOCK ||
            mle->type == DLM_MLE_MIGRATION) {
                if (namelen != mle->u.name.len ||
                    memcmp(name, mle->u.name.name, namelen)!=0)
                        return 0;
        } else {
                res = mle->u.res;
                if (namelen != res->lockname.len ||
                    memcmp(res->lockname.name, name, namelen) != 0)
                        return 0;
        }
        return 1;
}

#if 0
/* Code here is included but defined out as it aids debugging */

#define dlm_print_nodemap(m)  _dlm_print_nodemap(m,#m)
void _dlm_print_nodemap(unsigned long *map, const char *mapname)
{
        int i;
        printk("%s=[ ", mapname);
        for (i=0; i<O2NM_MAX_NODES; i++)
                if (test_bit(i, map))
                        printk("%d ", i);
        printk("]");
}

void dlm_print_one_mle(struct dlm_master_list_entry *mle)
{
        int refs;
        char *type;
        char attached;
        u8 master;
        unsigned int namelen;
        const char *name;
        struct kref *k;
        unsigned long *maybe = mle->maybe_map,
                      *vote = mle->vote_map,
                      *resp = mle->response_map,
                      *node = mle->node_map;

        k = &mle->mle_refs;
        if (mle->type == DLM_MLE_BLOCK)
                type = "BLK";
        else if (mle->type == DLM_MLE_MASTER)
                type = "MAS";
        else
                type = "MIG";
        refs = atomic_read(&k->refcount);
        master = mle->master;
        attached = (list_empty(&mle->hb_events) ? 'N' : 'Y');

        if (mle->type != DLM_MLE_MASTER) {
                namelen = mle->u.name.len;
                name = mle->u.name.name;
        } else {
                namelen = mle->u.res->lockname.len;
                name = mle->u.res->lockname.name;
        }

        mlog(ML_NOTICE, "%.*s: %3s refs=%3d mas=%3u new=%3u evt=%c inuse=%d ",
                  namelen, name, type, refs, master, mle->new_master, attached,
                  mle->inuse);
        dlm_print_nodemap(maybe);
        printk(", ");
        dlm_print_nodemap(vote);
        printk(", ");
        dlm_print_nodemap(resp);
        printk(", ");
        dlm_print_nodemap(node);
        printk(", ");
        printk("\n");
}

static void dlm_dump_mles(struct dlm_ctxt *dlm)
{
        struct dlm_master_list_entry *mle;
        struct list_head *iter;
        
        mlog(ML_NOTICE, "dumping all mles for domain %s:\n", dlm->name);
        spin_lock(&dlm->master_lock);
        list_for_each(iter, &dlm->master_list) {
                mle = list_entry(iter, struct dlm_master_list_entry, list);
                dlm_print_one_mle(mle);
        }
        spin_unlock(&dlm->master_lock);
}

int dlm_dump_all_mles(const char __user *data, unsigned int len)
{
        struct list_head *iter;
        struct dlm_ctxt *dlm;

        spin_lock(&dlm_domain_lock);
        list_for_each(iter, &dlm_domains) {
                dlm = list_entry (iter, struct dlm_ctxt, list);
                mlog(ML_NOTICE, "found dlm: %p, name=%s\n", dlm, dlm->name);
                dlm_dump_mles(dlm);
        }
        spin_unlock(&dlm_domain_lock);
        return len;
}
EXPORT_SYMBOL_GPL(dlm_dump_all_mles);

#endif  /*  0  */


static kmem_cache_t *dlm_mle_cache = NULL;


static void dlm_mle_release(struct kref *kref);
static void dlm_init_mle(struct dlm_master_list_entry *mle,
                        enum dlm_mle_type type,
                        struct dlm_ctxt *dlm,
                        struct dlm_lock_resource *res,
                        const char *name,
                        unsigned int namelen);
static void dlm_put_mle(struct dlm_master_list_entry *mle);
static void __dlm_put_mle(struct dlm_master_list_entry *mle);
static int dlm_find_mle(struct dlm_ctxt *dlm,
                        struct dlm_master_list_entry **mle,
                        char *name, unsigned int namelen);

static int dlm_do_master_request(struct dlm_master_list_entry *mle, int to);


static int dlm_wait_for_lock_mastery(struct dlm_ctxt *dlm,
                                     struct dlm_lock_resource *res,
                                     struct dlm_master_list_entry *mle,
                                     int *blocked);
static int dlm_restart_lock_mastery(struct dlm_ctxt *dlm,
                                    struct dlm_lock_resource *res,
                                    struct dlm_master_list_entry *mle,
                                    int blocked);
static int dlm_add_migration_mle(struct dlm_ctxt *dlm,
                                 struct dlm_lock_resource *res,
                                 struct dlm_master_list_entry *mle,
                                 struct dlm_master_list_entry **oldmle,
                                 const char *name, unsigned int namelen,
                                 u8 new_master, u8 master);

static u8 dlm_pick_migration_target(struct dlm_ctxt *dlm,
                                    struct dlm_lock_resource *res);
static void dlm_remove_nonlocal_locks(struct dlm_ctxt *dlm,
                                      struct dlm_lock_resource *res);
static int dlm_mark_lockres_migrating(struct dlm_ctxt *dlm,
                                       struct dlm_lock_resource *res,
                                       u8 target);
static int dlm_pre_master_reco_lockres(struct dlm_ctxt *dlm,
                                       struct dlm_lock_resource *res);


int dlm_is_host_down(int errno)
{
        switch (errno) {
                case -EBADF:
                case -ECONNREFUSED:
                case -ENOTCONN:
                case -ECONNRESET:
                case -EPIPE:
                case -EHOSTDOWN:
                case -EHOSTUNREACH:
                case -ETIMEDOUT:
                case -ECONNABORTED:
                case -ENETDOWN:
                case -ENETUNREACH:
                case -ENETRESET:
                case -ESHUTDOWN:
                case -ENOPROTOOPT:
                case -EINVAL:   /* if returned from our tcp code,
                                   this means there is no socket */
                        return 1;
        }
        return 0;
}


/*
 * MASTER LIST FUNCTIONS
 */


/*
 * regarding master list entries and heartbeat callbacks:
 *
 * in order to avoid sleeping and allocation that occurs in
 * heartbeat, master list entries are simply attached to the
 * dlm's established heartbeat callbacks.  the mle is attached
 * when it is created, and since the dlm->spinlock is held at
 * that time, any heartbeat event will be properly discovered
 * by the mle.  the mle needs to be detached from the
 * dlm->mle_hb_events list as soon as heartbeat events are no
 * longer useful to the mle, and before the mle is freed.
 *
 * as a general rule, heartbeat events are no longer needed by
 * the mle once an "answer" regarding the lock master has been
 * received.
 */
static inline void __dlm_mle_attach_hb_events(struct dlm_ctxt *dlm,
                                              struct dlm_master_list_entry *mle)
{
        assert_spin_locked(&dlm->spinlock);

        list_add_tail(&mle->hb_events, &dlm->mle_hb_events);
}


static inline void __dlm_mle_detach_hb_events(struct dlm_ctxt *dlm,
                                              struct dlm_master_list_entry *mle)
{
        if (!list_empty(&mle->hb_events))
                list_del_init(&mle->hb_events);
}


static inline void dlm_mle_detach_hb_events(struct dlm_ctxt *dlm,
                                            struct dlm_master_list_entry *mle)
{
        spin_lock(&dlm->spinlock);
        __dlm_mle_detach_hb_events(dlm, mle);
        spin_unlock(&dlm->spinlock);
}

static void dlm_get_mle_inuse(struct dlm_master_list_entry *mle)
{
        struct dlm_ctxt *dlm;
        dlm = mle->dlm;

        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&dlm->master_lock);
        mle->inuse++;
        kref_get(&mle->mle_refs);
}

static void dlm_put_mle_inuse(struct dlm_master_list_entry *mle)
{
        struct dlm_ctxt *dlm;
        dlm = mle->dlm;

        spin_lock(&dlm->spinlock);
        spin_lock(&dlm->master_lock);
        mle->inuse--;
        __dlm_put_mle(mle);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

}

/* remove from list and free */
static void __dlm_put_mle(struct dlm_master_list_entry *mle)
{
        struct dlm_ctxt *dlm;
        dlm = mle->dlm;

        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&dlm->master_lock);
        if (!atomic_read(&mle->mle_refs.refcount)) {
                /* this may or may not crash, but who cares.
                 * it's a BUG. */
                mlog(ML_ERROR, "bad mle: %p\n", mle);
                dlm_print_one_mle(mle);
                BUG();
        } else
                kref_put(&mle->mle_refs, dlm_mle_release);
}


/* must not have any spinlocks coming in */
static void dlm_put_mle(struct dlm_master_list_entry *mle)
{
        struct dlm_ctxt *dlm;
        dlm = mle->dlm;

        spin_lock(&dlm->spinlock);
        spin_lock(&dlm->master_lock);
        __dlm_put_mle(mle);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);
}

static inline void dlm_get_mle(struct dlm_master_list_entry *mle)
{
        kref_get(&mle->mle_refs);
}

static void dlm_init_mle(struct dlm_master_list_entry *mle,
                        enum dlm_mle_type type,
                        struct dlm_ctxt *dlm,
                        struct dlm_lock_resource *res,
                        const char *name,
                        unsigned int namelen)
{
        assert_spin_locked(&dlm->spinlock);

        mle->dlm = dlm;
        mle->type = type;
        INIT_LIST_HEAD(&mle->list);
        INIT_LIST_HEAD(&mle->hb_events);
        memset(mle->maybe_map, 0, sizeof(mle->maybe_map));
        spin_lock_init(&mle->spinlock);
        init_waitqueue_head(&mle->wq);
        atomic_set(&mle->woken, 0);
        kref_init(&mle->mle_refs);
        memset(mle->response_map, 0, sizeof(mle->response_map));
        mle->master = O2NM_MAX_NODES;
        mle->new_master = O2NM_MAX_NODES;
        mle->inuse = 0;

        if (mle->type == DLM_MLE_MASTER) {
                BUG_ON(!res);
                mle->u.res = res;
        } else if (mle->type == DLM_MLE_BLOCK) {
                BUG_ON(!name);
                memcpy(mle->u.name.name, name, namelen);
                mle->u.name.len = namelen;
        } else /* DLM_MLE_MIGRATION */ {
                BUG_ON(!name);
                memcpy(mle->u.name.name, name, namelen);
                mle->u.name.len = namelen;
        }

        /* copy off the node_map and register hb callbacks on our copy */
        memcpy(mle->node_map, dlm->domain_map, sizeof(mle->node_map));
        memcpy(mle->vote_map, dlm->domain_map, sizeof(mle->vote_map));
        clear_bit(dlm->node_num, mle->vote_map);
        clear_bit(dlm->node_num, mle->node_map);

        /* attach the mle to the domain node up/down events */
        __dlm_mle_attach_hb_events(dlm, mle);
}


/* returns 1 if found, 0 if not */
static int dlm_find_mle(struct dlm_ctxt *dlm,
                        struct dlm_master_list_entry **mle,
                        char *name, unsigned int namelen)
{
        struct dlm_master_list_entry *tmpmle;
        struct list_head *iter;

        assert_spin_locked(&dlm->master_lock);

        list_for_each(iter, &dlm->master_list) {
                tmpmle = list_entry(iter, struct dlm_master_list_entry, list);
                if (!dlm_mle_equal(dlm, tmpmle, name, namelen))
                        continue;
                dlm_get_mle(tmpmle);
                *mle = tmpmle;
                return 1;
        }
        return 0;
}

void dlm_hb_event_notify_attached(struct dlm_ctxt *dlm, int idx, int node_up)
{
        struct dlm_master_list_entry *mle;
        struct list_head *iter;

        assert_spin_locked(&dlm->spinlock);
        
        list_for_each(iter, &dlm->mle_hb_events) {
                mle = list_entry(iter, struct dlm_master_list_entry, 
                                 hb_events);
                if (node_up)
                        dlm_mle_node_up(dlm, mle, NULL, idx);
                else
                        dlm_mle_node_down(dlm, mle, NULL, idx);
        }
}

static void dlm_mle_node_down(struct dlm_ctxt *dlm,
                              struct dlm_master_list_entry *mle,
                              struct o2nm_node *node, int idx)
{
        spin_lock(&mle->spinlock);

        if (!test_bit(idx, mle->node_map))
                mlog(0, "node %u already removed from nodemap!\n", idx);
        else
                clear_bit(idx, mle->node_map);

        spin_unlock(&mle->spinlock);
}

static void dlm_mle_node_up(struct dlm_ctxt *dlm,
                            struct dlm_master_list_entry *mle,
                            struct o2nm_node *node, int idx)
{
        spin_lock(&mle->spinlock);

        if (test_bit(idx, mle->node_map))
                mlog(0, "node %u already in node map!\n", idx);
        else
                set_bit(idx, mle->node_map);

        spin_unlock(&mle->spinlock);
}


int dlm_init_mle_cache(void)
{
        dlm_mle_cache = kmem_cache_create("dlm_mle_cache",
                                          sizeof(struct dlm_master_list_entry),
                                          0, SLAB_HWCACHE_ALIGN,
                                          NULL, NULL);
        if (dlm_mle_cache == NULL)
                return -ENOMEM;
        return 0;
}

void dlm_destroy_mle_cache(void)
{
        if (dlm_mle_cache)
                kmem_cache_destroy(dlm_mle_cache);
}

static void dlm_mle_release(struct kref *kref)
{
        struct dlm_master_list_entry *mle;
        struct dlm_ctxt *dlm;

        mlog_entry_void();

        mle = container_of(kref, struct dlm_master_list_entry, mle_refs);
        dlm = mle->dlm;

        if (mle->type != DLM_MLE_MASTER) {
                mlog(0, "calling mle_release for %.*s, type %d\n",
                     mle->u.name.len, mle->u.name.name, mle->type);
        } else {
                mlog(0, "calling mle_release for %.*s, type %d\n",
                     mle->u.res->lockname.len,
                     mle->u.res->lockname.name, mle->type);
        }
        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&dlm->master_lock);

        /* remove from list if not already */
        if (!list_empty(&mle->list))
                list_del_init(&mle->list);

        /* detach the mle from the domain node up/down events */
        __dlm_mle_detach_hb_events(dlm, mle);

        /* NOTE: kfree under spinlock here.
         * if this is bad, we can move this to a freelist. */
        kmem_cache_free(dlm_mle_cache, mle);
}


/*
 * LOCK RESOURCE FUNCTIONS
 */

static void dlm_set_lockres_owner(struct dlm_ctxt *dlm,
                                  struct dlm_lock_resource *res,
                                  u8 owner)
{
        assert_spin_locked(&res->spinlock);

        mlog_entry("%.*s, %u\n", res->lockname.len, res->lockname.name, owner);

        if (owner == dlm->node_num)
                atomic_inc(&dlm->local_resources);
        else if (owner == DLM_LOCK_RES_OWNER_UNKNOWN)
                atomic_inc(&dlm->unknown_resources);
        else
                atomic_inc(&dlm->remote_resources);

        res->owner = owner;
}

void dlm_change_lockres_owner(struct dlm_ctxt *dlm,
                              struct dlm_lock_resource *res, u8 owner)
{
        assert_spin_locked(&res->spinlock);

        if (owner == res->owner)
                return;

        if (res->owner == dlm->node_num)
                atomic_dec(&dlm->local_resources);
        else if (res->owner == DLM_LOCK_RES_OWNER_UNKNOWN)
                atomic_dec(&dlm->unknown_resources);
        else
                atomic_dec(&dlm->remote_resources);

        dlm_set_lockres_owner(dlm, res, owner);
}


static void dlm_lockres_release(struct kref *kref)
{
        struct dlm_lock_resource *res;

        res = container_of(kref, struct dlm_lock_resource, refs);

        /* This should not happen -- all lockres' have a name
         * associated with them at init time. */
        BUG_ON(!res->lockname.name);

        mlog(0, "destroying lockres %.*s\n", res->lockname.len,
             res->lockname.name);

        /* By the time we're ready to blow this guy away, we shouldn't
         * be on any lists. */
        BUG_ON(!hlist_unhashed(&res->hash_node));
        BUG_ON(!list_empty(&res->granted));
        BUG_ON(!list_empty(&res->converting));
        BUG_ON(!list_empty(&res->blocked));
        BUG_ON(!list_empty(&res->dirty));
        BUG_ON(!list_empty(&res->recovering));
        BUG_ON(!list_empty(&res->purge));

        kfree(res->lockname.name);

        kfree(res);
}

void dlm_lockres_put(struct dlm_lock_resource *res)
{
        kref_put(&res->refs, dlm_lockres_release);
}

static void dlm_init_lockres(struct dlm_ctxt *dlm,
                             struct dlm_lock_resource *res,
                             const char *name, unsigned int namelen)
{
        char *qname;

        /* If we memset here, we lose our reference to the kmalloc'd
         * res->lockname.name, so be sure to init every field
         * correctly! */

        qname = (char *) res->lockname.name;
        memcpy(qname, name, namelen);

        res->lockname.len = namelen;
        res->lockname.hash = dlm_lockid_hash(name, namelen);

        init_waitqueue_head(&res->wq);
        spin_lock_init(&res->spinlock);
        INIT_HLIST_NODE(&res->hash_node);
        INIT_LIST_HEAD(&res->granted);
        INIT_LIST_HEAD(&res->converting);
        INIT_LIST_HEAD(&res->blocked);
        INIT_LIST_HEAD(&res->dirty);
        INIT_LIST_HEAD(&res->recovering);
        INIT_LIST_HEAD(&res->purge);
        atomic_set(&res->asts_reserved, 0);
        res->migration_pending = 0;

        kref_init(&res->refs);

        /* just for consistency */
        spin_lock(&res->spinlock);
        dlm_set_lockres_owner(dlm, res, DLM_LOCK_RES_OWNER_UNKNOWN);
        spin_unlock(&res->spinlock);

        res->state = DLM_LOCK_RES_IN_PROGRESS;

        res->last_used = 0;

        memset(res->lvb, 0, DLM_LVB_LEN);
}

struct dlm_lock_resource *dlm_new_lockres(struct dlm_ctxt *dlm,
                                   const char *name,
                                   unsigned int namelen)
{
        struct dlm_lock_resource *res;

        res = kmalloc(sizeof(struct dlm_lock_resource), GFP_KERNEL);
        if (!res)
                return NULL;

        res->lockname.name = kmalloc(namelen, GFP_KERNEL);
        if (!res->lockname.name) {
                kfree(res);
                return NULL;
        }

        dlm_init_lockres(dlm, res, name, namelen);
        return res;
}

/*
 * lookup a lock resource by name.
 * may already exist in the hashtable.
 * lockid is null terminated
 *
 * if not, allocate enough for the lockres and for
 * the temporary structure used in doing the mastering.
 *
 * also, do a lookup in the dlm->master_list to see
 * if another node has begun mastering the same lock.
 * if so, there should be a block entry in there
 * for this name, and we should *not* attempt to master
 * the lock here.   need to wait around for that node
 * to assert_master (or die).
 *
 */
struct dlm_lock_resource * dlm_get_lock_resource(struct dlm_ctxt *dlm,
                                          const char *lockid,
                                          int flags)
{
        struct dlm_lock_resource *tmpres=NULL, *res=NULL;
        struct dlm_master_list_entry *mle = NULL;
        struct dlm_master_list_entry *alloc_mle = NULL;
        int blocked = 0;
        int ret, nodenum;
        struct dlm_node_iter iter;
        unsigned int namelen, hash;
        int tries = 0;
        int bit, wait_on_recovery = 0;

        BUG_ON(!lockid);

        namelen = strlen(lockid);
        hash = dlm_lockid_hash(lockid, namelen);

        mlog(0, "get lockres %s (len %d)\n", lockid, namelen);

lookup:
        spin_lock(&dlm->spinlock);
        tmpres = __dlm_lookup_lockres(dlm, lockid, namelen, hash);
        if (tmpres) {
                spin_unlock(&dlm->spinlock);
                mlog(0, "found in hash!\n");
                if (res)
                        dlm_lockres_put(res);
                res = tmpres;
                goto leave;
        }

        if (!res) {
                spin_unlock(&dlm->spinlock);
                mlog(0, "allocating a new resource\n");
                /* nothing found and we need to allocate one. */
                alloc_mle = (struct dlm_master_list_entry *)
                        kmem_cache_alloc(dlm_mle_cache, GFP_KERNEL);
                if (!alloc_mle)
                        goto leave;
                res = dlm_new_lockres(dlm, lockid, namelen);
                if (!res)
                        goto leave;
                goto lookup;
        }

        mlog(0, "no lockres found, allocated our own: %p\n", res);

        if (flags & LKM_LOCAL) {
                /* caller knows it's safe to assume it's not mastered elsewhere
                 * DONE!  return right away */
                spin_lock(&res->spinlock);
                dlm_change_lockres_owner(dlm, res, dlm->node_num);
                __dlm_insert_lockres(dlm, res);
                spin_unlock(&res->spinlock);
                spin_unlock(&dlm->spinlock);
                /* lockres still marked IN_PROGRESS */
                goto wake_waiters;
        }

        /* check master list to see if another node has started mastering it */
        spin_lock(&dlm->master_lock);

        /* if we found a block, wait for lock to be mastered by another node */
        blocked = dlm_find_mle(dlm, &mle, (char *)lockid, namelen);
        if (blocked) {
                if (mle->type == DLM_MLE_MASTER) {
                        mlog(ML_ERROR, "master entry for nonexistent lock!\n");
                        BUG();
                } else if (mle->type == DLM_MLE_MIGRATION) {
                        /* migration is in progress! */
                        /* the good news is that we now know the
                         * "current" master (mle->master). */

                        spin_unlock(&dlm->master_lock);
                        assert_spin_locked(&dlm->spinlock);

                        /* set the lockres owner and hash it */
                        spin_lock(&res->spinlock);
                        dlm_set_lockres_owner(dlm, res, mle->master);
                        __dlm_insert_lockres(dlm, res);
                        spin_unlock(&res->spinlock);
                        spin_unlock(&dlm->spinlock);

                        /* master is known, detach */
                        dlm_mle_detach_hb_events(dlm, mle);
                        dlm_put_mle(mle);
                        mle = NULL;
                        goto wake_waiters;
                }
        } else {
                /* go ahead and try to master lock on this node */
                mle = alloc_mle;
                /* make sure this does not get freed below */
                alloc_mle = NULL;
                dlm_init_mle(mle, DLM_MLE_MASTER, dlm, res, NULL, 0);
                set_bit(dlm->node_num, mle->maybe_map);
                list_add(&mle->list, &dlm->master_list);

                /* still holding the dlm spinlock, check the recovery map
                 * to see if there are any nodes that still need to be 
                 * considered.  these will not appear in the mle nodemap
                 * but they might own this lockres.  wait on them. */
                bit = find_next_bit(dlm->recovery_map, O2NM_MAX_NODES, 0);
                if (bit < O2NM_MAX_NODES) {
                        mlog(ML_NOTICE, "%s:%.*s: at least one node (%d) to"
                             "recover before lock mastery can begin\n",
                             dlm->name, namelen, (char *)lockid, bit);
                        wait_on_recovery = 1;
                }
        }

        /* at this point there is either a DLM_MLE_BLOCK or a
         * DLM_MLE_MASTER on the master list, so it's safe to add the
         * lockres to the hashtable.  anyone who finds the lock will
         * still have to wait on the IN_PROGRESS. */

        /* finally add the lockres to its hash bucket */
        __dlm_insert_lockres(dlm, res);
        /* get an extra ref on the mle in case this is a BLOCK
         * if so, the creator of the BLOCK may try to put the last
         * ref at this time in the assert master handler, so we
         * need an extra one to keep from a bad ptr deref. */
        dlm_get_mle_inuse(mle);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        while (wait_on_recovery) {
                /* any cluster changes that occurred after dropping the
                 * dlm spinlock would be detectable be a change on the mle,
                 * so we only need to clear out the recovery map once. */
                if (dlm_is_recovery_lock(lockid, namelen)) {
                        mlog(ML_NOTICE, "%s: recovery map is not empty, but "
                             "must master $RECOVERY lock now\n", dlm->name);
                        if (!dlm_pre_master_reco_lockres(dlm, res))
                                wait_on_recovery = 0;
                        else {
                                mlog(0, "%s: waiting 500ms for heartbeat state "
                                    "change\n", dlm->name);
                                msleep(500);
                        }
                        continue;
                } 

                dlm_kick_recovery_thread(dlm);
                msleep(100);
                dlm_wait_for_recovery(dlm);

                spin_lock(&dlm->spinlock);
                bit = find_next_bit(dlm->recovery_map, O2NM_MAX_NODES, 0);
                if (bit < O2NM_MAX_NODES) {
                        mlog(ML_NOTICE, "%s:%.*s: at least one node (%d) to"
                             "recover before lock mastery can begin\n",
                             dlm->name, namelen, (char *)lockid, bit);
                        wait_on_recovery = 1;
                } else
                        wait_on_recovery = 0;
                spin_unlock(&dlm->spinlock);
        }

        /* must wait for lock to be mastered elsewhere */
        if (blocked)
                goto wait;

redo_request:
        ret = -EINVAL;
        dlm_node_iter_init(mle->vote_map, &iter);
        while ((nodenum = dlm_node_iter_next(&iter)) >= 0) {
                ret = dlm_do_master_request(mle, nodenum);
                if (ret < 0)
                        mlog_errno(ret);
                if (mle->master != O2NM_MAX_NODES) {
                        /* found a master ! */
                        if (mle->master <= nodenum)
                                break;
                        /* if our master request has not reached the master
                         * yet, keep going until it does.  this is how the
                         * master will know that asserts are needed back to
                         * the lower nodes. */
                        mlog(0, "%s:%.*s: requests only up to %u but master "
                             "is %u, keep going\n", dlm->name, namelen,
                             lockid, nodenum, mle->master);
                }
        }

wait:
        /* keep going until the response map includes all nodes */
        ret = dlm_wait_for_lock_mastery(dlm, res, mle, &blocked);
        if (ret < 0) {
                mlog(0, "%s:%.*s: node map changed, redo the "
                     "master request now, blocked=%d\n",
                     dlm->name, res->lockname.len,
                     res->lockname.name, blocked);
                if (++tries > 20) {
                        mlog(ML_ERROR, "%s:%.*s: spinning on "
                             "dlm_wait_for_lock_mastery, blocked=%d\n", 
                             dlm->name, res->lockname.len, 
                             res->lockname.name, blocked);
                        dlm_print_one_lock_resource(res);
                        /* dlm_print_one_mle(mle); */
                        tries = 0;
                }
                goto redo_request;
        }

        mlog(0, "lockres mastered by %u\n", res->owner);
        /* make sure we never continue without this */
        BUG_ON(res->owner == O2NM_MAX_NODES);

        /* master is known, detach if not already detached */
        dlm_mle_detach_hb_events(dlm, mle);
        dlm_put_mle(mle);
        /* put the extra ref */
        dlm_put_mle_inuse(mle);

wake_waiters:
        spin_lock(&res->spinlock);
        res->state &= ~DLM_LOCK_RES_IN_PROGRESS;
        spin_unlock(&res->spinlock);
        wake_up(&res->wq);

leave:
        /* need to free the unused mle */
        if (alloc_mle)
                kmem_cache_free(dlm_mle_cache, alloc_mle);

        return res;
}


#define DLM_MASTERY_TIMEOUT_MS   5000

static int dlm_wait_for_lock_mastery(struct dlm_ctxt *dlm,
                                     struct dlm_lock_resource *res,
                                     struct dlm_master_list_entry *mle,
                                     int *blocked)
{
        u8 m;
        int ret, bit;
        int map_changed, voting_done;
        int assert, sleep;

recheck:
        ret = 0;
        assert = 0;

        /* check if another node has already become the owner */
        spin_lock(&res->spinlock);
        if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
                mlog(0, "%s:%.*s: owner is suddenly %u\n", dlm->name,
                     res->lockname.len, res->lockname.name, res->owner);
                spin_unlock(&res->spinlock);
                /* this will cause the master to re-assert across
                 * the whole cluster, freeing up mles */
                ret = dlm_do_master_request(mle, res->owner);
                if (ret < 0) {
                        /* give recovery a chance to run */
                        mlog(ML_ERROR, "link to %u went down?: %d\n", res->owner, ret);
                        msleep(500);
                        goto recheck;
                }
                ret = 0;
                goto leave;
        }
        spin_unlock(&res->spinlock);

        spin_lock(&mle->spinlock);
        m = mle->master;
        map_changed = (memcmp(mle->vote_map, mle->node_map,
                              sizeof(mle->vote_map)) != 0);
        voting_done = (memcmp(mle->vote_map, mle->response_map,
                             sizeof(mle->vote_map)) == 0);

        /* restart if we hit any errors */
        if (map_changed) {
                int b;
                mlog(0, "%s: %.*s: node map changed, restarting\n",
                     dlm->name, res->lockname.len, res->lockname.name);
                ret = dlm_restart_lock_mastery(dlm, res, mle, *blocked);
                b = (mle->type == DLM_MLE_BLOCK);
                if ((*blocked && !b) || (!*blocked && b)) {
                        mlog(0, "%s:%.*s: status change: old=%d new=%d\n", 
                             dlm->name, res->lockname.len, res->lockname.name,
                             *blocked, b);
                        *blocked = b;
                }
                spin_unlock(&mle->spinlock);
                if (ret < 0) {
                        mlog_errno(ret);
                        goto leave;
                }
                mlog(0, "%s:%.*s: restart lock mastery succeeded, "
                     "rechecking now\n", dlm->name, res->lockname.len,
                     res->lockname.name);
                goto recheck;
        } else {
                if (!voting_done) {
                        mlog(0, "map not changed and voting not done "
                             "for %s:%.*s\n", dlm->name, res->lockname.len,
                             res->lockname.name);
                }
        }

        if (m != O2NM_MAX_NODES) {
                /* another node has done an assert!
                 * all done! */
                sleep = 0;
        } else {
                sleep = 1;
                /* have all nodes responded? */
                if (voting_done && !*blocked) {
                        bit = find_next_bit(mle->maybe_map, O2NM_MAX_NODES, 0);
                        if (dlm->node_num <= bit) {
                                /* my node number is lowest.
                                 * now tell other nodes that I am
                                 * mastering this. */
                                mle->master = dlm->node_num;
                                assert = 1;
                                sleep = 0;
                        }
                        /* if voting is done, but we have not received
                         * an assert master yet, we must sleep */
                }
        }

        spin_unlock(&mle->spinlock);

        /* sleep if we haven't finished voting yet */
        if (sleep) {
                unsigned long timeo = msecs_to_jiffies(DLM_MASTERY_TIMEOUT_MS);

                /*
                if (atomic_read(&mle->mle_refs.refcount) < 2)
                        mlog(ML_ERROR, "mle (%p) refs=%d, name=%.*s\n", mle,
                        atomic_read(&mle->mle_refs.refcount),
                        res->lockname.len, res->lockname.name);
                */
                atomic_set(&mle->woken, 0);
                (void)wait_event_timeout(mle->wq,
                                         (atomic_read(&mle->woken) == 1),
                                         timeo);
                if (res->owner == O2NM_MAX_NODES) {
                        mlog(0, "waiting again\n");
                        goto recheck;
                }
                mlog(0, "done waiting, master is %u\n", res->owner);
                ret = 0;
                goto leave;
        }

        ret = 0;   /* done */
        if (assert) {
                m = dlm->node_num;
                mlog(0, "about to master %.*s here, this=%u\n",
                     res->lockname.len, res->lockname.name, m);
                ret = dlm_do_assert_master(dlm, res->lockname.name,
                                           res->lockname.len, mle->vote_map, 0);
                if (ret) {
                        /* This is a failure in the network path,
                         * not in the response to the assert_master
                         * (any nonzero response is a BUG on this node).
                         * Most likely a socket just got disconnected
                         * due to node death. */
                        mlog_errno(ret);
                }
                /* no longer need to restart lock mastery.
                 * all living nodes have been contacted. */
                ret = 0;
        }

        /* set the lockres owner */
        spin_lock(&res->spinlock);
        dlm_change_lockres_owner(dlm, res, m);
        spin_unlock(&res->spinlock);

leave:
        return ret;
}

struct dlm_bitmap_diff_iter
{
        int curnode;
        unsigned long *orig_bm;
        unsigned long *cur_bm;
        unsigned long diff_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
};

enum dlm_node_state_change
{
        NODE_DOWN = -1,
        NODE_NO_CHANGE = 0,
        NODE_UP
};

static void dlm_bitmap_diff_iter_init(struct dlm_bitmap_diff_iter *iter,
                                      unsigned long *orig_bm,
                                      unsigned long *cur_bm)
{
        unsigned long p1, p2;
        int i;

        iter->curnode = -1;
        iter->orig_bm = orig_bm;
        iter->cur_bm = cur_bm;

        for (i = 0; i < BITS_TO_LONGS(O2NM_MAX_NODES); i++) {
                p1 = *(iter->orig_bm + i);
                p2 = *(iter->cur_bm + i);
                iter->diff_bm[i] = (p1 & ~p2) | (p2 & ~p1);
        }
}

static int dlm_bitmap_diff_iter_next(struct dlm_bitmap_diff_iter *iter,
                                     enum dlm_node_state_change *state)
{
        int bit;

        if (iter->curnode >= O2NM_MAX_NODES)
                return -ENOENT;

        bit = find_next_bit(iter->diff_bm, O2NM_MAX_NODES,
                            iter->curnode+1);
        if (bit >= O2NM_MAX_NODES) {
                iter->curnode = O2NM_MAX_NODES;
                return -ENOENT;
        }

        /* if it was there in the original then this node died */
        if (test_bit(bit, iter->orig_bm))
                *state = NODE_DOWN;
        else
                *state = NODE_UP;

        iter->curnode = bit;
        return bit;
}


static int dlm_restart_lock_mastery(struct dlm_ctxt *dlm,
                                    struct dlm_lock_resource *res,
                                    struct dlm_master_list_entry *mle,
                                    int blocked)
{
        struct dlm_bitmap_diff_iter bdi;
        enum dlm_node_state_change sc;
        int node;
        int ret = 0;

        mlog(0, "something happened such that the "
             "master process may need to be restarted!\n");

        assert_spin_locked(&mle->spinlock);

        dlm_bitmap_diff_iter_init(&bdi, mle->vote_map, mle->node_map);
        node = dlm_bitmap_diff_iter_next(&bdi, &sc);
        while (node >= 0) {
                if (sc == NODE_UP) {
                        /* a node came up.  clear any old vote from
                         * the response map and set it in the vote map
                         * then restart the mastery. */
                        mlog(ML_NOTICE, "node %d up while restarting\n", node);

                        /* redo the master request, but only for the new node */
                        mlog(0, "sending request to new node\n");
                        clear_bit(node, mle->response_map);
                        set_bit(node, mle->vote_map);
                } else {
                        mlog(ML_ERROR, "node down! %d\n", node);

                        /* if the node wasn't involved in mastery skip it,
                         * but clear it out from the maps so that it will
                         * not affect mastery of this lockres */
                        clear_bit(node, mle->response_map);
                        clear_bit(node, mle->vote_map);
                        if (!test_bit(node, mle->maybe_map))
                                goto next;

                        /* if we're already blocked on lock mastery, and the
                         * dead node wasn't the expected master, or there is
                         * another node in the maybe_map, keep waiting */
                        if (blocked) {
                                int lowest = find_next_bit(mle->maybe_map,
                                                       O2NM_MAX_NODES, 0);

                                /* act like it was never there */
                                clear_bit(node, mle->maybe_map);

                                if (node != lowest)
                                        goto next;

                                mlog(ML_ERROR, "expected master %u died while "
                                     "this node was blocked waiting on it!\n",
                                     node);
                                lowest = find_next_bit(mle->maybe_map,
                                                       O2NM_MAX_NODES,
                                                       lowest+1);
                                if (lowest < O2NM_MAX_NODES) {
                                        mlog(0, "still blocked. waiting "
                                             "on %u now\n", lowest);
                                        goto next;
                                }

                                /* mle is an MLE_BLOCK, but there is now
                                 * nothing left to block on.  we need to return
                                 * all the way back out and try again with
                                 * an MLE_MASTER. dlm_do_local_recovery_cleanup
                                 * has already run, so the mle refcount is ok */
                                mlog(0, "no longer blocking. we can "
                                     "try to master this here\n");
                                mle->type = DLM_MLE_MASTER;
                                memset(mle->maybe_map, 0,
                                       sizeof(mle->maybe_map));
                                memset(mle->response_map, 0,
                                       sizeof(mle->maybe_map));
                                memcpy(mle->vote_map, mle->node_map,
                                       sizeof(mle->node_map));
                                mle->u.res = res;
                                set_bit(dlm->node_num, mle->maybe_map);

                                ret = -EAGAIN;
                                goto next;
                        }

                        clear_bit(node, mle->maybe_map);
                        if (node > dlm->node_num)
                                goto next;

                        mlog(0, "dead node in map!\n");
                        /* yuck. go back and re-contact all nodes
                         * in the vote_map, removing this node. */
                        memset(mle->response_map, 0,
                               sizeof(mle->response_map));
                }
                ret = -EAGAIN;
next:
                node = dlm_bitmap_diff_iter_next(&bdi, &sc);
        }
        return ret;
}


/*
 * DLM_MASTER_REQUEST_MSG
 *
 * returns: 0 on success,
 *          -errno on a network error
 *
 * on error, the caller should assume the target node is "dead"
 *
 */

static int dlm_do_master_request(struct dlm_master_list_entry *mle, int to)
{
        struct dlm_ctxt *dlm = mle->dlm;
        struct dlm_master_request request;
        int ret, response=0, resend;

        memset(&request, 0, sizeof(request));
        request.node_idx = dlm->node_num;

        BUG_ON(mle->type == DLM_MLE_MIGRATION);

        if (mle->type != DLM_MLE_MASTER) {
                request.namelen = mle->u.name.len;
                memcpy(request.name, mle->u.name.name, request.namelen);
        } else {
                request.namelen = mle->u.res->lockname.len;
                memcpy(request.name, mle->u.res->lockname.name,
                        request.namelen);
        }

again:
        ret = o2net_send_message(DLM_MASTER_REQUEST_MSG, dlm->key, &request,
                                 sizeof(request), to, &response);
        if (ret < 0)  {
                if (ret == -ESRCH) {
                        /* should never happen */
                        mlog(ML_ERROR, "TCP stack not ready!\n");
                        BUG();
                } else if (ret == -EINVAL) {
                        mlog(ML_ERROR, "bad args passed to o2net!\n");
                        BUG();
                } else if (ret == -ENOMEM) {
                        mlog(ML_ERROR, "out of memory while trying to send "
                             "network message!  retrying\n");
                        /* this is totally crude */
                        msleep(50);
                        goto again;
                } else if (!dlm_is_host_down(ret)) {
                        /* not a network error. bad. */
                        mlog_errno(ret);
                        mlog(ML_ERROR, "unhandled error!");
                        BUG();
                }
                /* all other errors should be network errors,
                 * and likely indicate node death */
                mlog(ML_ERROR, "link to %d went down!\n", to);
                goto out;
        }

        ret = 0;
        resend = 0;
        spin_lock(&mle->spinlock);
        switch (response) {
                case DLM_MASTER_RESP_YES:
                        set_bit(to, mle->response_map);
                        mlog(0, "node %u is the master, response=YES\n", to);
                        mle->master = to;
                        break;
                case DLM_MASTER_RESP_NO:
                        mlog(0, "node %u not master, response=NO\n", to);
                        set_bit(to, mle->response_map);
                        break;
                case DLM_MASTER_RESP_MAYBE:
                        mlog(0, "node %u not master, response=MAYBE\n", to);
                        set_bit(to, mle->response_map);
                        set_bit(to, mle->maybe_map);
                        break;
                case DLM_MASTER_RESP_ERROR:
                        mlog(0, "node %u hit an error, resending\n", to);
                        resend = 1;
                        response = 0;
                        break;
                default:
                        mlog(ML_ERROR, "bad response! %u\n", response);
                        BUG();
        }
        spin_unlock(&mle->spinlock);
        if (resend) {
                /* this is also totally crude */
                msleep(50);
                goto again;
        }

out:
        return ret;
}

/*
 * locks that can be taken here:
 * dlm->spinlock
 * res->spinlock
 * mle->spinlock
 * dlm->master_list
 *
 * if possible, TRIM THIS DOWN!!!
 */
int dlm_master_request_handler(struct o2net_msg *msg, u32 len, void *data)
{
        u8 response = DLM_MASTER_RESP_MAYBE;
        struct dlm_ctxt *dlm = data;
        struct dlm_lock_resource *res = NULL;
        struct dlm_master_request *request = (struct dlm_master_request *) msg->buf;
        struct dlm_master_list_entry *mle = NULL, *tmpmle = NULL;
        char *name;
        unsigned int namelen, hash;
        int found, ret;
        int set_maybe;
        int dispatch_assert = 0;

        if (!dlm_grab(dlm))
                return DLM_MASTER_RESP_NO;

        if (!dlm_domain_fully_joined(dlm)) {
                response = DLM_MASTER_RESP_NO;
                goto send_response;
        }

        name = request->name;
        namelen = request->namelen;
        hash = dlm_lockid_hash(name, namelen);

        if (namelen > DLM_LOCKID_NAME_MAX) {
                response = DLM_IVBUFLEN;
                goto send_response;
        }

way_up_top:
        spin_lock(&dlm->spinlock);
        res = __dlm_lookup_lockres(dlm, name, namelen, hash);
        if (res) {
                spin_unlock(&dlm->spinlock);

                /* take care of the easy cases up front */
                spin_lock(&res->spinlock);
                if (res->state & DLM_LOCK_RES_RECOVERING) {
                        spin_unlock(&res->spinlock);
                        mlog(0, "returning DLM_MASTER_RESP_ERROR since res is "
                             "being recovered\n");
                        response = DLM_MASTER_RESP_ERROR;
                        if (mle)
                                kmem_cache_free(dlm_mle_cache, mle);
                        goto send_response;
                }

                if (res->owner == dlm->node_num) {
                        spin_unlock(&res->spinlock);
                        // mlog(0, "this node is the master\n");
                        response = DLM_MASTER_RESP_YES;
                        if (mle)
                                kmem_cache_free(dlm_mle_cache, mle);

                        /* this node is the owner.
                         * there is some extra work that needs to
                         * happen now.  the requesting node has
                         * caused all nodes up to this one to
                         * create mles.  this node now needs to
                         * go back and clean those up. */
                        dispatch_assert = 1;
                        goto send_response;
                } else if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
                        spin_unlock(&res->spinlock);
                        // mlog(0, "node %u is the master\n", res->owner);
                        response = DLM_MASTER_RESP_NO;
                        if (mle)
                                kmem_cache_free(dlm_mle_cache, mle);
                        goto send_response;
                }

                /* ok, there is no owner.  either this node is
                 * being blocked, or it is actively trying to
                 * master this lock. */
                if (!(res->state & DLM_LOCK_RES_IN_PROGRESS)) {
                        mlog(ML_ERROR, "lock with no owner should be "
                             "in-progress!\n");
                        BUG();
                }

                // mlog(0, "lockres is in progress...\n");
                spin_lock(&dlm->master_lock);
                found = dlm_find_mle(dlm, &tmpmle, name, namelen);
                if (!found) {
                        mlog(ML_ERROR, "no mle found for this lock!\n");
                        BUG();
                }
                set_maybe = 1;
                spin_lock(&tmpmle->spinlock);
                if (tmpmle->type == DLM_MLE_BLOCK) {
                        // mlog(0, "this node is waiting for "
                        // "lockres to be mastered\n");
                        response = DLM_MASTER_RESP_NO;
                } else if (tmpmle->type == DLM_MLE_MIGRATION) {
                        mlog(0, "node %u is master, but trying to migrate to "
                             "node %u.\n", tmpmle->master, tmpmle->new_master);
                        if (tmpmle->master == dlm->node_num) {
                                response = DLM_MASTER_RESP_YES;
                                mlog(ML_ERROR, "no owner on lockres, but this "
                                     "node is trying to migrate it to %u?!\n",
                                     tmpmle->new_master);
                                BUG();
                        } else {
                                /* the real master can respond on its own */
                                response = DLM_MASTER_RESP_NO;
                        }
                } else if (tmpmle->master != DLM_LOCK_RES_OWNER_UNKNOWN) {
                        set_maybe = 0;
                        if (tmpmle->master == dlm->node_num) {
                                response = DLM_MASTER_RESP_YES;
                                /* this node will be the owner.
                                 * go back and clean the mles on any
                                 * other nodes */
                                dispatch_assert = 1;
                        } else
                                response = DLM_MASTER_RESP_NO;
                } else {
                        // mlog(0, "this node is attempting to "
                        // "master lockres\n");
                        response = DLM_MASTER_RESP_MAYBE;
                }
                if (set_maybe)
                        set_bit(request->node_idx, tmpmle->maybe_map);
                spin_unlock(&tmpmle->spinlock);

                spin_unlock(&dlm->master_lock);
                spin_unlock(&res->spinlock);

                /* keep the mle attached to heartbeat events */
                dlm_put_mle(tmpmle);
                if (mle)
                        kmem_cache_free(dlm_mle_cache, mle);
                goto send_response;
        }

        /*
         * lockres doesn't exist on this node
         * if there is an MLE_BLOCK, return NO
         * if there is an MLE_MASTER, return MAYBE
         * otherwise, add an MLE_BLOCK, return NO
         */
        spin_lock(&dlm->master_lock);
        found = dlm_find_mle(dlm, &tmpmle, name, namelen);
        if (!found) {
                /* this lockid has never been seen on this node yet */
                // mlog(0, "no mle found\n");
                if (!mle) {
                        spin_unlock(&dlm->master_lock);
                        spin_unlock(&dlm->spinlock);

                        mle = (struct dlm_master_list_entry *)
                                kmem_cache_alloc(dlm_mle_cache, GFP_KERNEL);
                        if (!mle) {
                                response = DLM_MASTER_RESP_ERROR;
                                mlog_errno(-ENOMEM);
                                goto send_response;
                        }
                        goto way_up_top;
                }

                // mlog(0, "this is second time thru, already allocated, "
                // "add the block.\n");
                dlm_init_mle(mle, DLM_MLE_BLOCK, dlm, NULL, name, namelen);
                set_bit(request->node_idx, mle->maybe_map);
                list_add(&mle->list, &dlm->master_list);
                response = DLM_MASTER_RESP_NO;
        } else {
                // mlog(0, "mle was found\n");
                set_maybe = 1;
                spin_lock(&tmpmle->spinlock);
                if (tmpmle->master == dlm->node_num) {
                        mlog(ML_ERROR, "no lockres, but an mle with this node as master!\n");
                        BUG();
                }
                if (tmpmle->type == DLM_MLE_BLOCK)
                        response = DLM_MASTER_RESP_NO;
                else if (tmpmle->type == DLM_MLE_MIGRATION) {
                        mlog(0, "migration mle was found (%u->%u)\n",
                             tmpmle->master, tmpmle->new_master);
                        /* real master can respond on its own */
                        response = DLM_MASTER_RESP_NO;
                } else
                        response = DLM_MASTER_RESP_MAYBE;
                if (set_maybe)
                        set_bit(request->node_idx, tmpmle->maybe_map);
                spin_unlock(&tmpmle->spinlock);
        }
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        if (found) {
                /* keep the mle attached to heartbeat events */
                dlm_put_mle(tmpmle);
        }
send_response:

        if (dispatch_assert) {
                if (response != DLM_MASTER_RESP_YES)
                        mlog(ML_ERROR, "invalid response %d\n", response);
                if (!res) {
                        mlog(ML_ERROR, "bad lockres while trying to assert!\n");
                        BUG();
                }
                mlog(0, "%u is the owner of %.*s, cleaning everyone else\n",
                             dlm->node_num, res->lockname.len, res->lockname.name);
                ret = dlm_dispatch_assert_master(dlm, res, 0, request->node_idx, 
                                                 DLM_ASSERT_MASTER_MLE_CLEANUP);
                if (ret < 0) {
                        mlog(ML_ERROR, "failed to dispatch assert master work\n");
                        response = DLM_MASTER_RESP_ERROR;
                }
        }

        dlm_put(dlm);
        return response;
}

/*
 * DLM_ASSERT_MASTER_MSG
 */


/*
 * NOTE: this can be used for debugging
 * can periodically run all locks owned by this node
 * and re-assert across the cluster...
 */
static int dlm_do_assert_master(struct dlm_ctxt *dlm, const char *lockname,
                                unsigned int namelen, void *nodemap,
                                u32 flags)
{
        struct dlm_assert_master assert;
        int to, tmpret;
        struct dlm_node_iter iter;
        int ret = 0;
        int reassert;

        BUG_ON(namelen > O2NM_MAX_NAME_LEN);
again:
        reassert = 0;

        /* note that if this nodemap is empty, it returns 0 */
        dlm_node_iter_init(nodemap, &iter);
        while ((to = dlm_node_iter_next(&iter)) >= 0) {
                int r = 0;
                mlog(0, "sending assert master to %d (%.*s)\n", to,
                     namelen, lockname);
                memset(&assert, 0, sizeof(assert));
                assert.node_idx = dlm->node_num;
                assert.namelen = namelen;
                memcpy(assert.name, lockname, namelen);
                assert.flags = cpu_to_be32(flags);

                tmpret = o2net_send_message(DLM_ASSERT_MASTER_MSG, dlm->key,
                                            &assert, sizeof(assert), to, &r);
                if (tmpret < 0) {
                        mlog(ML_ERROR, "assert_master returned %d!\n", tmpret);
                        if (!dlm_is_host_down(tmpret)) {
                                mlog(ML_ERROR, "unhandled error!\n");
                                BUG();
                        }
                        /* a node died.  finish out the rest of the nodes. */
                        mlog(ML_ERROR, "link to %d went down!\n", to);
                        /* any nonzero status return will do */
                        ret = tmpret;
                } else if (r < 0) {
                        /* ok, something horribly messed.  kill thyself. */
                        mlog(ML_ERROR,"during assert master of %.*s to %u, "
                             "got %d.\n", namelen, lockname, to, r);
                        dlm_dump_lock_resources(dlm);
                        BUG();
                } else if (r == EAGAIN) {
                        mlog(0, "%.*s: node %u create mles on other "
                             "nodes and requests a re-assert\n", 
                             namelen, lockname, to);
                        reassert = 1;
                }
        }

        if (reassert)
                goto again;

        return ret;
}

/*
 * locks that can be taken here:
 * dlm->spinlock
 * res->spinlock
 * mle->spinlock
 * dlm->master_list
 *
 * if possible, TRIM THIS DOWN!!!
 */
int dlm_assert_master_handler(struct o2net_msg *msg, u32 len, void *data)
{
        struct dlm_ctxt *dlm = data;
        struct dlm_master_list_entry *mle = NULL;
        struct dlm_assert_master *assert = (struct dlm_assert_master *)msg->buf;
        struct dlm_lock_resource *res = NULL;
        char *name;
        unsigned int namelen, hash;
        u32 flags;
        int master_request = 0;
        int ret = 0;

        if (!dlm_grab(dlm))
                return 0;

        name = assert->name;
        namelen = assert->namelen;
        hash = dlm_lockid_hash(name, namelen);
        flags = be32_to_cpu(assert->flags);

        if (namelen > DLM_LOCKID_NAME_MAX) {
                mlog(ML_ERROR, "Invalid name length!");
                goto done;
        }

        spin_lock(&dlm->spinlock);

        if (flags)
                mlog(0, "assert_master with flags: %u\n", flags);

        /* find the MLE */
        spin_lock(&dlm->master_lock);
        if (!dlm_find_mle(dlm, &mle, name, namelen)) {
                /* not an error, could be master just re-asserting */
                mlog(0, "just got an assert_master from %u, but no "
                     "MLE for it! (%.*s)\n", assert->node_idx,
                     namelen, name);
        } else {
                int bit = find_next_bit (mle->maybe_map, O2NM_MAX_NODES, 0);
                if (bit >= O2NM_MAX_NODES) {
                        /* not necessarily an error, though less likely.
                         * could be master just re-asserting. */
                        mlog(0, "no bits set in the maybe_map, but %u "
                             "is asserting! (%.*s)\n", assert->node_idx,
                             namelen, name);
                } else if (bit != assert->node_idx) {
                        if (flags & DLM_ASSERT_MASTER_MLE_CLEANUP) {
                                mlog(0, "master %u was found, %u should "
                                     "back off\n", assert->node_idx, bit);
                        } else {
                                /* with the fix for bug 569, a higher node
                                 * number winning the mastery will respond
                                 * YES to mastery requests, but this node
                                 * had no way of knowing.  let it pass. */
                                mlog(0, "%u is the lowest node, "
                                     "%u is asserting. (%.*s)  %u must "
                                     "have begun after %u won.\n", bit,
                                     assert->node_idx, namelen, name, bit,
                                     assert->node_idx);
                        }
                }
                if (mle->type == DLM_MLE_MIGRATION) {
                        if (flags & DLM_ASSERT_MASTER_MLE_CLEANUP) {
                                mlog(0, "%s:%.*s: got cleanup assert"
                                     " from %u for migration\n",
                                     dlm->name, namelen, name,
                                     assert->node_idx);
                        } else if (!(flags & DLM_ASSERT_MASTER_FINISH_MIGRATION)) {
                                mlog(0, "%s:%.*s: got unrelated assert"
                                     " from %u for migration, ignoring\n",
                                     dlm->name, namelen, name,
                                     assert->node_idx);
                                __dlm_put_mle(mle);
                                spin_unlock(&dlm->master_lock);
                                spin_unlock(&dlm->spinlock);
                                goto done;
                        }       
                }
        }
        spin_unlock(&dlm->master_lock);

        /* ok everything checks out with the MLE
         * now check to see if there is a lockres */
        res = __dlm_lookup_lockres(dlm, name, namelen, hash);
        if (res) {
                spin_lock(&res->spinlock);
                if (res->state & DLM_LOCK_RES_RECOVERING)  {
                        mlog(ML_ERROR, "%u asserting but %.*s is "
                             "RECOVERING!\n", assert->node_idx, namelen, name);
                        goto kill;
                }
                if (!mle) {
                        if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN &&
                            res->owner != assert->node_idx) {
                                mlog(ML_ERROR, "assert_master from "
                                          "%u, but current owner is "
                                          "%u! (%.*s)\n",
                                       assert->node_idx, res->owner,
                                       namelen, name);
                                goto kill;
                        }
                } else if (mle->type != DLM_MLE_MIGRATION) {
                        if (res->owner != DLM_LOCK_RES_OWNER_UNKNOWN) {
                                /* owner is just re-asserting */
                                if (res->owner == assert->node_idx) {
                                        mlog(0, "owner %u re-asserting on "
                                             "lock %.*s\n", assert->node_idx,
                                             namelen, name);
                                        goto ok;
                                }
                                mlog(ML_ERROR, "got assert_master from "
                                     "node %u, but %u is the owner! "
                                     "(%.*s)\n", assert->node_idx,
                                     res->owner, namelen, name);
                                goto kill;
                        }
                        if (!(res->state & DLM_LOCK_RES_IN_PROGRESS)) {
                                mlog(ML_ERROR, "got assert from %u, but lock "
                                     "with no owner should be "
                                     "in-progress! (%.*s)\n",
                                     assert->node_idx,
                                     namelen, name);
                                goto kill;
                        }
                } else /* mle->type == DLM_MLE_MIGRATION */ {
                        /* should only be getting an assert from new master */
                        if (assert->node_idx != mle->new_master) {
                                mlog(ML_ERROR, "got assert from %u, but "
                                     "new master is %u, and old master "
                                     "was %u (%.*s)\n",
                                     assert->node_idx, mle->new_master,
                                     mle->master, namelen, name);
                                goto kill;
                        }

                }
ok:
                spin_unlock(&res->spinlock);
        }
        spin_unlock(&dlm->spinlock);

        // mlog(0, "woo!  got an assert_master from node %u!\n",
        //           assert->node_idx);
        if (mle) {
                int extra_ref = 0;
                int nn = -1;
                int rr, err = 0;
                
                spin_lock(&mle->spinlock);
                if (mle->type == DLM_MLE_BLOCK || mle->type == DLM_MLE_MIGRATION)
                        extra_ref = 1;
                else {
                        /* MASTER mle: if any bits set in the response map
                         * then the calling node needs to re-assert to clear
                         * up nodes that this node contacted */
                        while ((nn = find_next_bit (mle->response_map, O2NM_MAX_NODES, 
                                                    nn+1)) < O2NM_MAX_NODES) {
                                if (nn != dlm->node_num && nn != assert->node_idx)
                                        master_request = 1;
                        }
                }
                mle->master = assert->node_idx;
                atomic_set(&mle->woken, 1);
                wake_up(&mle->wq);
                spin_unlock(&mle->spinlock);

                if (res) {
                        spin_lock(&res->spinlock);
                        if (mle->type == DLM_MLE_MIGRATION) {
                                mlog(0, "finishing off migration of lockres %.*s, "
                                        "from %u to %u\n",
                                        res->lockname.len, res->lockname.name,
                                        dlm->node_num, mle->new_master);
                                res->state &= ~DLM_LOCK_RES_MIGRATING;
                                dlm_change_lockres_owner(dlm, res, mle->new_master);
                                BUG_ON(res->state & DLM_LOCK_RES_DIRTY);
                        } else {
                                dlm_change_lockres_owner(dlm, res, mle->master);
                        }
                        spin_unlock(&res->spinlock);
                }

                /* master is known, detach if not already detached.
                 * ensures that only one assert_master call will happen
                 * on this mle. */
                spin_lock(&dlm->spinlock);
                spin_lock(&dlm->master_lock);

                rr = atomic_read(&mle->mle_refs.refcount);
                if (mle->inuse > 0) {
                        if (extra_ref && rr < 3)
                                err = 1;
                        else if (!extra_ref && rr < 2)
                                err = 1;
                } else {
                        if (extra_ref && rr < 2)
                                err = 1;
                        else if (!extra_ref && rr < 1)
                                err = 1;
                }
                if (err) {
                        mlog(ML_ERROR, "%s:%.*s: got assert master from %u "
                             "that will mess up this node, refs=%d, extra=%d, "
                             "inuse=%d\n", dlm->name, namelen, name,
                             assert->node_idx, rr, extra_ref, mle->inuse);
                        dlm_print_one_mle(mle);
                }
                list_del_init(&mle->list);
                __dlm_mle_detach_hb_events(dlm, mle);
                __dlm_put_mle(mle);
                if (extra_ref) {
                        /* the assert master message now balances the extra
                         * ref given by the master / migration request message.
                         * if this is the last put, it will be removed
                         * from the list. */
                        __dlm_put_mle(mle);
                }
                spin_unlock(&dlm->master_lock);
                spin_unlock(&dlm->spinlock);
        } else if (res) {
                if (res->owner != assert->node_idx) {
                        mlog(0, "assert_master from %u, but current "
                             "owner is %u (%.*s), no mle\n", assert->node_idx,
                             res->owner, namelen, name);
                }
        }

done:
        ret = 0;
        if (res)
                dlm_lockres_put(res);
        dlm_put(dlm);
        if (master_request) {
                mlog(0, "need to tell master to reassert\n");
                ret = EAGAIN;  // positive. negative would shoot down the node.
        }
        return ret;

kill:
        /* kill the caller! */
        spin_unlock(&res->spinlock);
        spin_unlock(&dlm->spinlock);
        dlm_lockres_put(res);
        mlog(ML_ERROR, "Bad message received from another node.  Dumping state "
             "and killing the other node now!  This node is OK and can continue.\n");
        dlm_dump_lock_resources(dlm);
        dlm_put(dlm);
        return -EINVAL;
}

int dlm_dispatch_assert_master(struct dlm_ctxt *dlm,
                               struct dlm_lock_resource *res,
                               int ignore_higher, u8 request_from, u32 flags)
{
        struct dlm_work_item *item;
        item = kcalloc(1, sizeof(*item), GFP_KERNEL);
        if (!item)
                return -ENOMEM;


        /* queue up work for dlm_assert_master_worker */
        dlm_grab(dlm);  /* get an extra ref for the work item */
        dlm_init_work_item(dlm, item, dlm_assert_master_worker, NULL);
        item->u.am.lockres = res; /* already have a ref */
        /* can optionally ignore node numbers higher than this node */
        item->u.am.ignore_higher = ignore_higher;
        item->u.am.request_from = request_from;
        item->u.am.flags = flags;

        if (ignore_higher) 
                mlog(0, "IGNORE HIGHER: %.*s\n", res->lockname.len, 
                     res->lockname.name);
                
        spin_lock(&dlm->work_lock);
        list_add_tail(&item->list, &dlm->work_list);
        spin_unlock(&dlm->work_lock);

        schedule_work(&dlm->dispatched_work);
        return 0;
}

static void dlm_assert_master_worker(struct dlm_work_item *item, void *data)
{
        struct dlm_ctxt *dlm = data;
        int ret = 0;
        struct dlm_lock_resource *res;
        unsigned long nodemap[BITS_TO_LONGS(O2NM_MAX_NODES)];
        int ignore_higher;
        int bit;
        u8 request_from;
        u32 flags;

        dlm = item->dlm;
        res = item->u.am.lockres;
        ignore_higher = item->u.am.ignore_higher;
        request_from = item->u.am.request_from;
        flags = item->u.am.flags;

        spin_lock(&dlm->spinlock);
        memcpy(nodemap, dlm->domain_map, sizeof(nodemap));
        spin_unlock(&dlm->spinlock);

        clear_bit(dlm->node_num, nodemap);
        if (ignore_higher) {
                /* if is this just to clear up mles for nodes below
                 * this node, do not send the message to the original
                 * caller or any node number higher than this */
                clear_bit(request_from, nodemap);
                bit = dlm->node_num;
                while (1) {
                        bit = find_next_bit(nodemap, O2NM_MAX_NODES,
                                            bit+1);
                        if (bit >= O2NM_MAX_NODES)
                                break;
                        clear_bit(bit, nodemap);
                }
        }

        /* this call now finishes out the nodemap
         * even if one or more nodes die */
        mlog(0, "worker about to master %.*s here, this=%u\n",
                     res->lockname.len, res->lockname.name, dlm->node_num);
        ret = dlm_do_assert_master(dlm, res->lockname.name,
                                   res->lockname.len,
                                   nodemap, flags);
        if (ret < 0) {
                /* no need to restart, we are done */
                mlog_errno(ret);
        }

        dlm_lockres_put(res);

        mlog(0, "finished with dlm_assert_master_worker\n");
}

/* SPECIAL CASE for the $RECOVERY lock used by the recovery thread.
 * We cannot wait for node recovery to complete to begin mastering this
 * lockres because this lockres is used to kick off recovery! ;-)
 * So, do a pre-check on all living nodes to see if any of those nodes
 * think that $RECOVERY is currently mastered by a dead node.  If so,
 * we wait a short time to allow that node to get notified by its own
 * heartbeat stack, then check again.  All $RECOVERY lock resources
 * mastered by dead nodes are purged when the hearbeat callback is 
 * fired, so we can know for sure that it is safe to continue once
 * the node returns a live node or no node.  */
static int dlm_pre_master_reco_lockres(struct dlm_ctxt *dlm,
                                       struct dlm_lock_resource *res)
{
        struct dlm_node_iter iter;
        int nodenum;
        int ret = 0;
        u8 master = DLM_LOCK_RES_OWNER_UNKNOWN;

        spin_lock(&dlm->spinlock);
        dlm_node_iter_init(dlm->domain_map, &iter);
        spin_unlock(&dlm->spinlock);

        while ((nodenum = dlm_node_iter_next(&iter)) >= 0) {
                /* do not send to self */
                if (nodenum == dlm->node_num)
                        continue;
                ret = dlm_do_master_requery(dlm, res, nodenum, &master);
                if (ret < 0) {
                        mlog_errno(ret);
                        if (!dlm_is_host_down(ret))
                                BUG();
                        /* host is down, so answer for that node would be
                         * DLM_LOCK_RES_OWNER_UNKNOWN.  continue. */
                }

                if (master != DLM_LOCK_RES_OWNER_UNKNOWN) {
                        /* check to see if this master is in the recovery map */
                        spin_lock(&dlm->spinlock);
                        if (test_bit(master, dlm->recovery_map)) {
                                mlog(ML_NOTICE, "%s: node %u has not seen "
                                     "node %u go down yet, and thinks the "
                                     "dead node is mastering the recovery "
                                     "lock.  must wait.\n", dlm->name,
                                     nodenum, master);
                                ret = -EAGAIN;
                        }
                        spin_unlock(&dlm->spinlock);
                        mlog(0, "%s: reco lock master is %u\n", dlm->name, 
                             master);
                        break;
                }
        }
        return ret;
}


/*
 * DLM_MIGRATE_LOCKRES
 */


int dlm_migrate_lockres(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
                        u8 target)
{
        struct dlm_master_list_entry *mle = NULL;
        struct dlm_master_list_entry *oldmle = NULL;
        struct dlm_migratable_lockres *mres = NULL;
        int ret = -EINVAL;
        const char *name;
        unsigned int namelen;
        int mle_added = 0;
        struct list_head *queue, *iter;
        int i;
        struct dlm_lock *lock;
        int empty = 1;

        if (!dlm_grab(dlm))
                return -EINVAL;

        name = res->lockname.name;
        namelen = res->lockname.len;

        mlog(0, "migrating %.*s to %u\n", namelen, name, target);

        /*
         * ensure this lockres is a proper candidate for migration
         */
        spin_lock(&res->spinlock);
        if (res->owner == DLM_LOCK_RES_OWNER_UNKNOWN) {
                mlog(0, "cannot migrate lockres with unknown owner!\n");
                spin_unlock(&res->spinlock);
                goto leave;
        }
        if (res->owner != dlm->node_num) {
                mlog(0, "cannot migrate lockres this node doesn't own!\n");
                spin_unlock(&res->spinlock);
                goto leave;
        }
        mlog(0, "checking queues...\n");
        queue = &res->granted;
        for (i=0; i<3; i++) {
                list_for_each(iter, queue) {
                        lock = list_entry (iter, struct dlm_lock, list);
                        empty = 0;
                        if (lock->ml.node == dlm->node_num) {
                                mlog(0, "found a lock owned by this node "
                                     "still on the %s queue!  will not "
                                     "migrate this lockres\n",
                                     i==0 ? "granted" :
                                     (i==1 ? "converting" : "blocked"));
                                spin_unlock(&res->spinlock);
                                ret = -ENOTEMPTY;
                                goto leave;
                        }
                }
                queue++;
        }
        mlog(0, "all locks on this lockres are nonlocal.  continuing\n");
        spin_unlock(&res->spinlock);

        /* no work to do */
        if (empty) {
                mlog(0, "no locks were found on this lockres! done!\n");
                ret = 0;
                goto leave;
        }

        /*
         * preallocate up front
         * if this fails, abort
         */

        ret = -ENOMEM;
        mres = (struct dlm_migratable_lockres *) __get_free_page(GFP_KERNEL);
        if (!mres) {
                mlog_errno(ret);
                goto leave;
        }

        mle = (struct dlm_master_list_entry *) kmem_cache_alloc(dlm_mle_cache,
                                                                GFP_KERNEL);
        if (!mle) {
                mlog_errno(ret);
                goto leave;
        }
        ret = 0;

        /*
         * find a node to migrate the lockres to
         */

        mlog(0, "picking a migration node\n");
        spin_lock(&dlm->spinlock);
        /* pick a new node */
        if (!test_bit(target, dlm->domain_map) ||
            target >= O2NM_MAX_NODES) {
                target = dlm_pick_migration_target(dlm, res);
        }
        mlog(0, "node %u chosen for migration\n", target);

        if (target >= O2NM_MAX_NODES ||
            !test_bit(target, dlm->domain_map)) {
                /* target chosen is not alive */
                ret = -EINVAL;
        }

        if (ret) {
                spin_unlock(&dlm->spinlock);
                goto fail;
        }

        mlog(0, "continuing with target = %u\n", target);

        /*
         * clear any existing master requests and
         * add the migration mle to the list
         */
        spin_lock(&dlm->master_lock);
        ret = dlm_add_migration_mle(dlm, res, mle, &oldmle, name,
                                    namelen, target, dlm->node_num);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        if (ret == -EEXIST) {
                mlog(0, "another process is already migrating it\n");
                goto fail;
        }
        mle_added = 1;

        /*
         * set the MIGRATING flag and flush asts
         * if we fail after this we need to re-dirty the lockres
         */
        if (dlm_mark_lockres_migrating(dlm, res, target) < 0) {
                mlog(ML_ERROR, "tried to migrate %.*s to %u, but "
                     "the target went down.\n", res->lockname.len,
                     res->lockname.name, target);
                spin_lock(&res->spinlock);
                res->state &= ~DLM_LOCK_RES_MIGRATING;
                spin_unlock(&res->spinlock);
                ret = -EINVAL;
        }

fail:
        if (oldmle) {
                /* master is known, detach if not already detached */
                dlm_mle_detach_hb_events(dlm, oldmle);
                dlm_put_mle(oldmle);
        }

        if (ret < 0) {
                if (mle_added) {
                        dlm_mle_detach_hb_events(dlm, mle);
                        dlm_put_mle(mle);
                } else if (mle) {
                        kmem_cache_free(dlm_mle_cache, mle);
                }
                goto leave;
        }

        /*
         * at this point, we have a migration target, an mle
         * in the master list, and the MIGRATING flag set on
         * the lockres
         */


        /* get an extra reference on the mle.
         * otherwise the assert_master from the new
         * master will destroy this.
         * also, make sure that all callers of dlm_get_mle
         * take both dlm->spinlock and dlm->master_lock */
        spin_lock(&dlm->spinlock);
        spin_lock(&dlm->master_lock);
        dlm_get_mle_inuse(mle);
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        /* notify new node and send all lock state */
        /* call send_one_lockres with migration flag.
         * this serves as notice to the target node that a
         * migration is starting. */
        ret = dlm_send_one_lockres(dlm, res, mres, target,
                                   DLM_MRES_MIGRATION);

        if (ret < 0) {
                mlog(0, "migration to node %u failed with %d\n",
                     target, ret);
                /* migration failed, detach and clean up mle */
                dlm_mle_detach_hb_events(dlm, mle);
                dlm_put_mle(mle);
                dlm_put_mle_inuse(mle);
                spin_lock(&res->spinlock);
                res->state &= ~DLM_LOCK_RES_MIGRATING;
                spin_unlock(&res->spinlock);
                goto leave;
        }

        /* at this point, the target sends a message to all nodes,
         * (using dlm_do_migrate_request).  this node is skipped since
         * we had to put an mle in the list to begin the process.  this
         * node now waits for target to do an assert master.  this node
         * will be the last one notified, ensuring that the migration
         * is complete everywhere.  if the target dies while this is
         * going on, some nodes could potentially see the target as the
         * master, so it is important that my recovery finds the migration
         * mle and sets the master to UNKNONWN. */


        /* wait for new node to assert master */
        while (1) {
                ret = wait_event_interruptible_timeout(mle->wq,
                                        (atomic_read(&mle->woken) == 1),
                                        msecs_to_jiffies(5000));

                if (ret >= 0) {
                        if (atomic_read(&mle->woken) == 1 ||
                            res->owner == target)
                                break;

                        mlog(0, "timed out during migration\n");
                        /* avoid hang during shutdown when migrating lockres 
                         * to a node which also goes down */
                        if (dlm_is_node_dead(dlm, target)) {
                                mlog(0, "%s:%.*s: expected migration "
                                     "target %u is no longer up, restarting\n",
                                     dlm->name, res->lockname.len,
                                     res->lockname.name, target);
                                ret = -ERESTARTSYS;
                        }
                }
                if (ret == -ERESTARTSYS) {
                        /* migration failed, detach and clean up mle */
                        dlm_mle_detach_hb_events(dlm, mle);
                        dlm_put_mle(mle);
                        dlm_put_mle_inuse(mle);
                        spin_lock(&res->spinlock);
                        res->state &= ~DLM_LOCK_RES_MIGRATING;
                        spin_unlock(&res->spinlock);
                        goto leave;
                }
                /* TODO: if node died: stop, clean up, return error */
        }

        /* all done, set the owner, clear the flag */
        spin_lock(&res->spinlock);
        dlm_set_lockres_owner(dlm, res, target);
        res->state &= ~DLM_LOCK_RES_MIGRATING;
        dlm_remove_nonlocal_locks(dlm, res);
        spin_unlock(&res->spinlock);
        wake_up(&res->wq);

        /* master is known, detach if not already detached */
        dlm_mle_detach_hb_events(dlm, mle);
        dlm_put_mle_inuse(mle);
        ret = 0;

        dlm_lockres_calc_usage(dlm, res);

leave:
        /* re-dirty the lockres if we failed */
        if (ret < 0)
                dlm_kick_thread(dlm, res);

        /* TODO: cleanup */
        if (mres)
                free_page((unsigned long)mres);

        dlm_put(dlm);

        mlog(0, "returning %d\n", ret);
        return ret;
}
EXPORT_SYMBOL_GPL(dlm_migrate_lockres);

int dlm_lock_basts_flushed(struct dlm_ctxt *dlm, struct dlm_lock *lock)
{
        int ret;
        spin_lock(&dlm->ast_lock);
        spin_lock(&lock->spinlock);
        ret = (list_empty(&lock->bast_list) && !lock->bast_pending);
        spin_unlock(&lock->spinlock);
        spin_unlock(&dlm->ast_lock);
        return ret;
}

static int dlm_migration_can_proceed(struct dlm_ctxt *dlm,
                                     struct dlm_lock_resource *res,
                                     u8 mig_target)
{
        int can_proceed;
        spin_lock(&res->spinlock);
        can_proceed = !!(res->state & DLM_LOCK_RES_MIGRATING);
        spin_unlock(&res->spinlock);

        /* target has died, so make the caller break out of the 
         * wait_event, but caller must recheck the domain_map */
        spin_lock(&dlm->spinlock);
        if (!test_bit(mig_target, dlm->domain_map))
                can_proceed = 1;
        spin_unlock(&dlm->spinlock);
        return can_proceed;
}

int dlm_lockres_is_dirty(struct dlm_ctxt *dlm, struct dlm_lock_resource *res)
{
        int ret;
        spin_lock(&res->spinlock);
        ret = !!(res->state & DLM_LOCK_RES_DIRTY);
        spin_unlock(&res->spinlock);
        return ret;
}


static int dlm_mark_lockres_migrating(struct dlm_ctxt *dlm,
                                       struct dlm_lock_resource *res,
                                       u8 target)
{
        int ret = 0;

        mlog(0, "dlm_mark_lockres_migrating: %.*s, from %u to %u\n",
               res->lockname.len, res->lockname.name, dlm->node_num,
               target);
        /* need to set MIGRATING flag on lockres.  this is done by
         * ensuring that all asts have been flushed for this lockres. */
        spin_lock(&res->spinlock);
        BUG_ON(res->migration_pending);
        res->migration_pending = 1;
        /* strategy is to reserve an extra ast then release
         * it below, letting the release do all of the work */
        __dlm_lockres_reserve_ast(res);
        spin_unlock(&res->spinlock);

        /* now flush all the pending asts.. hang out for a bit */
        dlm_kick_thread(dlm, res);
        wait_event(dlm->ast_wq, !dlm_lockres_is_dirty(dlm, res));
        dlm_lockres_release_ast(dlm, res);

        mlog(0, "about to wait on migration_wq, dirty=%s\n",
               res->state & DLM_LOCK_RES_DIRTY ? "yes" : "no");
        /* if the extra ref we just put was the final one, this
         * will pass thru immediately.  otherwise, we need to wait
         * for the last ast to finish. */
again:
        ret = wait_event_interruptible_timeout(dlm->migration_wq,
                   dlm_migration_can_proceed(dlm, res, target),
                   msecs_to_jiffies(1000));
        if (ret < 0) {
                mlog(0, "woken again: migrating? %s, dead? %s\n",
                       res->state & DLM_LOCK_RES_MIGRATING ? "yes":"no",
                       test_bit(target, dlm->domain_map) ? "no":"yes");
        } else {
                mlog(0, "all is well: migrating? %s, dead? %s\n",
                       res->state & DLM_LOCK_RES_MIGRATING ? "yes":"no",
                       test_bit(target, dlm->domain_map) ? "no":"yes");
        }
        if (!dlm_migration_can_proceed(dlm, res, target)) {
                mlog(0, "trying again...\n");
                goto again;
        }

        /* did the target go down or die? */
        spin_lock(&dlm->spinlock);
        if (!test_bit(target, dlm->domain_map)) {
                mlog(ML_ERROR, "aha. migration target %u just went down\n",
                     target);
                ret = -EHOSTDOWN;
        }
        spin_unlock(&dlm->spinlock);

        /*
         * at this point:
         *
         *   o the DLM_LOCK_RES_MIGRATING flag is set
         *   o there are no pending asts on this lockres
         *   o all processes trying to reserve an ast on this
         *     lockres must wait for the MIGRATING flag to clear
         */
        return ret;
}

/* last step in the migration process.
 * original master calls this to free all of the dlm_lock
 * structures that used to be for other nodes. */
static void dlm_remove_nonlocal_locks(struct dlm_ctxt *dlm,
                                      struct dlm_lock_resource *res)
{
        struct list_head *iter, *iter2;
        struct list_head *queue = &res->granted;
        int i;
        struct dlm_lock *lock;

        assert_spin_locked(&res->spinlock);

        BUG_ON(res->owner == dlm->node_num);

        for (i=0; i<3; i++) {
                list_for_each_safe(iter, iter2, queue) {
                        lock = list_entry (iter, struct dlm_lock, list);
                        if (lock->ml.node != dlm->node_num) {
                                mlog(0, "putting lock for node %u\n",
                                     lock->ml.node);
                                /* be extra careful */
                                BUG_ON(!list_empty(&lock->ast_list));
                                BUG_ON(!list_empty(&lock->bast_list));
                                BUG_ON(lock->ast_pending);
                                BUG_ON(lock->bast_pending);
                                list_del_init(&lock->list);
                                dlm_lock_put(lock);
                        }
                }
                queue++;
        }
}

/* for now this is not too intelligent.  we will
 * need stats to make this do the right thing.
 * this just finds the first lock on one of the
 * queues and uses that node as the target. */
static u8 dlm_pick_migration_target(struct dlm_ctxt *dlm,
                                    struct dlm_lock_resource *res)
{
        int i;
        struct list_head *queue = &res->granted;
        struct list_head *iter;
        struct dlm_lock *lock;
        int nodenum;

        assert_spin_locked(&dlm->spinlock);

        spin_lock(&res->spinlock);
        for (i=0; i<3; i++) {
                list_for_each(iter, queue) {
                        /* up to the caller to make sure this node
                         * is alive */
                        lock = list_entry (iter, struct dlm_lock, list);
                        if (lock->ml.node != dlm->node_num) {
                                spin_unlock(&res->spinlock);
                                return lock->ml.node;
                        }
                }
                queue++;
        }
        spin_unlock(&res->spinlock);
        mlog(0, "have not found a suitable target yet! checking domain map\n");

        /* ok now we're getting desperate.  pick anyone alive. */
        nodenum = -1;
        while (1) {
                nodenum = find_next_bit(dlm->domain_map,
                                        O2NM_MAX_NODES, nodenum+1);
                mlog(0, "found %d in domain map\n", nodenum);
                if (nodenum >= O2NM_MAX_NODES)
                        break;
                if (nodenum != dlm->node_num) {
                        mlog(0, "picking %d\n", nodenum);
                        return nodenum;
                }
        }

        mlog(0, "giving up.  no master to migrate to\n");
        return DLM_LOCK_RES_OWNER_UNKNOWN;
}



/* this is called by the new master once all lockres
 * data has been received */
static int dlm_do_migrate_request(struct dlm_ctxt *dlm,
                                  struct dlm_lock_resource *res,
                                  u8 master, u8 new_master,
                                  struct dlm_node_iter *iter)
{
        struct dlm_migrate_request migrate;
        int ret, status = 0;
        int nodenum;

        memset(&migrate, 0, sizeof(migrate));
        migrate.namelen = res->lockname.len;
        memcpy(migrate.name, res->lockname.name, migrate.namelen);
        migrate.new_master = new_master;
        migrate.master = master;

        ret = 0;

        /* send message to all nodes, except the master and myself */
        while ((nodenum = dlm_node_iter_next(iter)) >= 0) {
                if (nodenum == master ||
                    nodenum == new_master)
                        continue;

                ret = o2net_send_message(DLM_MIGRATE_REQUEST_MSG, dlm->key,
                                         &migrate, sizeof(migrate), nodenum,
                                         &status);
                if (ret < 0)
                        mlog_errno(ret);
                else if (status < 0) {
                        mlog(0, "migrate request (node %u) returned %d!\n",
                             nodenum, status);
                        ret = status;
                }
        }

        if (ret < 0)
                mlog_errno(ret);

        mlog(0, "returning ret=%d\n", ret);
        return ret;
}


/* if there is an existing mle for this lockres, we now know who the master is.
 * (the one who sent us *this* message) we can clear it up right away.
 * since the process that put the mle on the list still has a reference to it,
 * we can unhash it now, set the master and wake the process.  as a result,
 * we will have no mle in the list to start with.  now we can add an mle for
 * the migration and this should be the only one found for those scanning the
 * list.  */
int dlm_migrate_request_handler(struct o2net_msg *msg, u32 len, void *data)
{
        struct dlm_ctxt *dlm = data;
        struct dlm_lock_resource *res = NULL;
        struct dlm_migrate_request *migrate = (struct dlm_migrate_request *) msg->buf;
        struct dlm_master_list_entry *mle = NULL, *oldmle = NULL;
        const char *name;
        unsigned int namelen, hash;
        int ret = 0;

        if (!dlm_grab(dlm))
                return -EINVAL;

        name = migrate->name;
        namelen = migrate->namelen;
        hash = dlm_lockid_hash(name, namelen);

        /* preallocate.. if this fails, abort */
        mle = (struct dlm_master_list_entry *) kmem_cache_alloc(dlm_mle_cache,
                                                         GFP_KERNEL);

        if (!mle) {
                ret = -ENOMEM;
                goto leave;
        }

        /* check for pre-existing lock */
        spin_lock(&dlm->spinlock);
        res = __dlm_lookup_lockres(dlm, name, namelen, hash);
        spin_lock(&dlm->master_lock);

        if (res) {
                spin_lock(&res->spinlock);
                if (res->state & DLM_LOCK_RES_RECOVERING) {
                        /* if all is working ok, this can only mean that we got
                        * a migrate request from a node that we now see as
                        * dead.  what can we do here?  drop it to the floor? */
                        spin_unlock(&res->spinlock);
                        mlog(ML_ERROR, "Got a migrate request, but the "
                             "lockres is marked as recovering!");
                        kmem_cache_free(dlm_mle_cache, mle);
                        ret = -EINVAL; /* need a better solution */
                        goto unlock;
                }
                res->state |= DLM_LOCK_RES_MIGRATING;
                spin_unlock(&res->spinlock);
        }

        /* ignore status.  only nonzero status would BUG. */
        ret = dlm_add_migration_mle(dlm, res, mle, &oldmle,
                                    name, namelen,
                                    migrate->new_master,
                                    migrate->master);

unlock:
        spin_unlock(&dlm->master_lock);
        spin_unlock(&dlm->spinlock);

        if (oldmle) {
                /* master is known, detach if not already detached */
                dlm_mle_detach_hb_events(dlm, oldmle);
                dlm_put_mle(oldmle);
        }

        if (res)
                dlm_lockres_put(res);
leave:
        dlm_put(dlm);
        return ret;
}

/* must be holding dlm->spinlock and dlm->master_lock
 * when adding a migration mle, we can clear any other mles
 * in the master list because we know with certainty that
 * the master is "master".  so we remove any old mle from
 * the list after setting it's master field, and then add
 * the new migration mle.  this way we can hold with the rule
 * of having only one mle for a given lock name at all times. */
static int dlm_add_migration_mle(struct dlm_ctxt *dlm,
                                 struct dlm_lock_resource *res,
                                 struct dlm_master_list_entry *mle,
                                 struct dlm_master_list_entry **oldmle,
                                 const char *name, unsigned int namelen,
                                 u8 new_master, u8 master)
{
        int found;
        int ret = 0;

        *oldmle = NULL;

        mlog_entry_void();

        assert_spin_locked(&dlm->spinlock);
        assert_spin_locked(&dlm->master_lock);

        /* caller is responsible for any ref taken here on oldmle */
        found = dlm_find_mle(dlm, oldmle, (char *)name, namelen);
        if (found) {
                struct dlm_master_list_entry *tmp = *oldmle;
                spin_lock(&tmp->spinlock);
                if (tmp->type == DLM_MLE_MIGRATION) {
                        if (master == dlm->node_num) {
                                /* ah another process raced me to it */
                                mlog(0, "tried to migrate %.*s, but some "
                                     "process beat me to it\n",
                                     namelen, name);
                                ret = -EEXIST;
                        } else {
                                /* bad.  2 NODES are trying to migrate! */
                                mlog(ML_ERROR, "migration error  mle: "
                                     "master=%u new_master=%u // request: "
                                     "master=%u new_master=%u // "
                                     "lockres=%.*s\n",
                                     tmp->master, tmp->new_master,
                                     master, new_master,
                                     namelen, name);
                                BUG();
                        }
                } else {
                        /* this is essentially what assert_master does */
                        tmp->master = master;
                        atomic_set(&tmp->woken, 1);
                        wake_up(&tmp->wq);
                        /* remove it from the list so that only one
                         * mle will be found */
                        list_del_init(&tmp->list);
                        __dlm_mle_detach_hb_events(dlm, mle);
                }
                spin_unlock(&tmp->spinlock);
        }

        /* now add a migration mle to the tail of the list */
        dlm_init_mle(mle, DLM_MLE_MIGRATION, dlm, res, name, namelen);
        mle->new_master = new_master;
        mle->master = master;
        /* do this for consistency with other mle types */
        set_bit(new_master, mle->maybe_map);
        list_add(&mle->list, &dlm->master_list);

        return ret;
}


void dlm_clean_master_list(struct dlm_ctxt *dlm, u8 dead_node)
{
        struct list_head *iter, *iter2;
        struct dlm_master_list_entry *mle;
        struct dlm_lock_resource *res;
        unsigned int hash;

        mlog_entry("dlm=%s, dead node=%u\n", dlm->name, dead_node);
top:
        assert_spin_locked(&dlm->spinlock);

        /* clean the master list */
        spin_lock(&dlm->master_lock);
        list_for_each_safe(iter, iter2, &dlm->master_list) {
                mle = list_entry(iter, struct dlm_master_list_entry, list);

                BUG_ON(mle->type != DLM_MLE_BLOCK &&
                       mle->type != DLM_MLE_MASTER &&
                       mle->type != DLM_MLE_MIGRATION);

                /* MASTER mles are initiated locally.  the waiting
                 * process will notice the node map change
                 * shortly.  let that happen as normal. */
                if (mle->type == DLM_MLE_MASTER)
                        continue;


                /* BLOCK mles are initiated by other nodes.
                 * need to clean up if the dead node would have
                 * been the master. */
                if (mle->type == DLM_MLE_BLOCK) {
                        int bit;

                        spin_lock(&mle->spinlock);
                        bit = find_next_bit(mle->maybe_map, O2NM_MAX_NODES, 0);
                        if (bit != dead_node) {
                                mlog(0, "mle found, but dead node %u would "
                                     "not have been master\n", dead_node);
                                spin_unlock(&mle->spinlock);
                        } else {
                                /* must drop the refcount by one since the
                                 * assert_master will never arrive.  this
                                 * may result in the mle being unlinked and
                                 * freed, but there may still be a process
                                 * waiting in the dlmlock path which is fine. */
                                mlog(ML_ERROR, "node %u was expected master\n",
                                     dead_node);
                                atomic_set(&mle->woken, 1);
                                spin_unlock(&mle->spinlock);
                                wake_up(&mle->wq);
                                /* do not need events any longer, so detach 
                                 * from heartbeat */
                                __dlm_mle_detach_hb_events(dlm, mle);
                                __dlm_put_mle(mle);
                        }
                        continue;
                }

                /* everything else is a MIGRATION mle */

                /* the rule for MIGRATION mles is that the master
                 * becomes UNKNOWN if *either* the original or
                 * the new master dies.  all UNKNOWN lockreses
                 * are sent to whichever node becomes the recovery
                 * master.  the new master is responsible for
                 * determining if there is still a master for
                 * this lockres, or if he needs to take over
                 * mastery.  either way, this node should expect
                 * another message to resolve this. */
                if (mle->master != dead_node &&
                    mle->new_master != dead_node)
                        continue;

                /* if we have reached this point, this mle needs to
                 * be removed from the list and freed. */

                /* remove from the list early.  NOTE: unlinking
                 * list_head while in list_for_each_safe */
                __dlm_mle_detach_hb_events(dlm, mle);
                spin_lock(&mle->spinlock);
                list_del_init(&mle->list);
                atomic_set(&mle->woken, 1);
                spin_unlock(&mle->spinlock);
                wake_up(&mle->wq);

                mlog(0, "%s: node %u died during migration from "
                     "%u to %u!\n", dlm->name, dead_node,
                     mle->master, mle->new_master);
                /* if there is a lockres associated with this
                 * mle, find it and set its owner to UNKNOWN */
                hash = dlm_lockid_hash(mle->u.name.name, mle->u.name.len);
                res = __dlm_lookup_lockres(dlm, mle->u.name.name,
                                           mle->u.name.len, hash);
                if (res) {
                        /* unfortunately if we hit this rare case, our
                         * lock ordering is messed.  we need to drop
                         * the master lock so that we can take the
                         * lockres lock, meaning that we will have to
                         * restart from the head of list. */
                        spin_unlock(&dlm->master_lock);

                        /* move lockres onto recovery list */
                        spin_lock(&res->spinlock);
                        dlm_set_lockres_owner(dlm, res,
                                        DLM_LOCK_RES_OWNER_UNKNOWN);
                        dlm_move_lockres_to_recovery_list(dlm, res);
                        spin_unlock(&res->spinlock);
                        dlm_lockres_put(res);

                        /* about to get rid of mle, detach from heartbeat */
                        __dlm_mle_detach_hb_events(dlm, mle);

                        /* dump the mle */
                        spin_lock(&dlm->master_lock);
                        __dlm_put_mle(mle);
                        spin_unlock(&dlm->master_lock);

                        /* restart */
                        goto top;
                }

                /* this may be the last reference */
                __dlm_put_mle(mle);
        }
        spin_unlock(&dlm->master_lock);
}


int dlm_finish_migration(struct dlm_ctxt *dlm, struct dlm_lock_resource *res,
                         u8 old_master)
{
        struct dlm_node_iter iter;
        int ret = 0;

        spin_lock(&dlm->spinlock);
        dlm_node_iter_init(dlm->domain_map, &iter);
        clear_bit(old_master, iter.node_map);
        clear_bit(dlm->node_num, iter.node_map);
        spin_unlock(&dlm->spinlock);

        mlog(0, "now time to do a migrate request to other nodes\n");
        ret = dlm_do_migrate_request(dlm, res, old_master,
                                     dlm->node_num, &iter);
        if (ret < 0) {
                mlog_errno(ret);
                goto leave;
        }

        mlog(0, "doing assert master of %.*s to all except the original node\n",
             res->lockname.len, res->lockname.name);
        /* this call now finishes out the nodemap
         * even if one or more nodes die */
        ret = dlm_do_assert_master(dlm, res->lockname.name,
                                   res->lockname.len, iter.node_map,
                                   DLM_ASSERT_MASTER_FINISH_MIGRATION);
        if (ret < 0) {
                /* no longer need to retry.  all living nodes contacted. */
                mlog_errno(ret);
                ret = 0;
        }

        memset(iter.node_map, 0, sizeof(iter.node_map));
        set_bit(old_master, iter.node_map);
        mlog(0, "doing assert master of %.*s back to %u\n",
             res->lockname.len, res->lockname.name, old_master);
        ret = dlm_do_assert_master(dlm, res->lockname.name,
                                   res->lockname.len, iter.node_map,
                                   DLM_ASSERT_MASTER_FINISH_MIGRATION);
        if (ret < 0) {
                mlog(0, "assert master to original master failed "
                     "with %d.\n", ret);
                /* the only nonzero status here would be because of
                 * a dead original node.  we're done. */
                ret = 0;
        }

        /* all done, set the owner, clear the flag */
        spin_lock(&res->spinlock);
        dlm_set_lockres_owner(dlm, res, dlm->node_num);
        res->state &= ~DLM_LOCK_RES_MIGRATING;
        spin_unlock(&res->spinlock);
        /* re-dirty it on the new master */
        dlm_kick_thread(dlm, res);
        wake_up(&res->wq);
leave:
        return ret;
}

/*
 * LOCKRES AST REFCOUNT
 * this is integral to migration
 */

/* for future intent to call an ast, reserve one ahead of time.
 * this should be called only after waiting on the lockres
 * with dlm_wait_on_lockres, and while still holding the
 * spinlock after the call. */
void __dlm_lockres_reserve_ast(struct dlm_lock_resource *res)
{
        assert_spin_locked(&res->spinlock);
        if (res->state & DLM_LOCK_RES_MIGRATING) {
                __dlm_print_one_lock_resource(res);
        }
        BUG_ON(res->state & DLM_LOCK_RES_MIGRATING);

        atomic_inc(&res->asts_reserved);
}

/*
 * used to drop the reserved ast, either because it went unused,
 * or because the ast/bast was actually called.
 *
 * also, if there is a pending migration on this lockres,
 * and this was the last pending ast on the lockres,
 * atomically set the MIGRATING flag before we drop the lock.
 * this is how we ensure that migration can proceed with no
 * asts in progress.  note that it is ok if the state of the
 * queues is such that a lock should be granted in the future
 * or that a bast should be fired, because the new master will
 * shuffle the lists on this lockres as soon as it is migrated.
 */
void dlm_lockres_release_ast(struct dlm_ctxt *dlm,
                             struct dlm_lock_resource *res)
{
        if (!atomic_dec_and_lock(&res->asts_reserved, &res->spinlock))
                return;

        if (!res->migration_pending) {
                spin_unlock(&res->spinlock);
                return;
        }

        BUG_ON(res->state & DLM_LOCK_RES_MIGRATING);
        res->migration_pending = 0;
        res->state |= DLM_LOCK_RES_MIGRATING;
        spin_unlock(&res->spinlock);
        wake_up(&res->wq);
        wake_up(&dlm->migration_wq);
}