markers: fix unregister bug and reenter bug

unregister bug:

codes using makers are typically calling marker_probe_unregister()
and then destroying the data that marker_probe_func needs(or
unloading this module). This is bug when the corresponding
marker_probe_func is still running(on other cpus),
it is using the destroying/ed data.

we should call synchronize_sched() after marker_update_probes().

reenter bug:

marker_probe_register(), marker_probe_unregister() and
marker_probe_unregister_private_data() are not reentrant safe
functions. these 3 functions release markers_mutex and then
require it again and do "entry->oldptr = old; ...", but entry->oldptr
maybe is using now for these 3 functions may reenter when markers_mutex
is released.

we use synchronize_sched() instead of call_rcu_sched() to fix
this bug. actually we can do:
"
if (entry->rcu_pending)
		rcu_barrier_sched();
"
after require markers_mutex again. but synchronize_sched()
is better and simpler. For these 3 functions are not critical path.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/marker.c b/kernel/marker.c
index 7d1faecd7a51bd643cc1e10f0f2048765136bf16..9f76c4a622ec13bb50250b9b73272a8d668d03ce 100644 (file)
--- a/kernel/marker.c
+++ b/kernel/marker.c
@@ -60,9 +60,6 @@ struct marker_entry {
        struct marker_probe_closure single;
        struct marker_probe_closure *multi;
        int refcount;   /* Number of times armed. 0 if disarmed. */
-       struct rcu_head rcu;
-       void *oldptr;
-       unsigned char rcu_pending:1;
        unsigned char ptype:1;
        char name[0];   /* Contains name'\0'format'\0' */
 };
@@ -199,16 +196,6 @@ void marker_probe_cb_noarg(const struct marker *mdata, void *call_private, ...)
 }
 EXPORT_SYMBOL_GPL(marker_probe_cb_noarg);
 
-static void free_old_closure(struct rcu_head *head)
-{
-       struct marker_entry *entry = container_of(head,
-               struct marker_entry, rcu);
-       kfree(entry->oldptr);
-       /* Make sure we free the data before setting the pending flag to 0 */
-       smp_wmb();
-       entry->rcu_pending = 0;
-}
-
 static void debug_print_probes(struct marker_entry *entry)
 {
        int i;
@@ -417,7 +404,6 @@ static struct marker_entry *add_marker(const char *name, const char *format)
        e->multi = NULL;
        e->ptype = 0;
        e->refcount = 0;
-       e->rcu_pending = 0;
        hlist_add_head(&e->hlist, head);
        return e;
 }
@@ -447,9 +433,6 @@ static int remove_marker(const char *name)
        if (e->single.func != __mark_empty_function)
                return -EBUSY;
        hlist_del(&e->hlist);
-       /* Make sure the call_rcu has been executed */
-       if (e->rcu_pending)
-               rcu_barrier_sched();
        kfree(e);
        return 0;
 }
@@ -479,12 +462,8 @@ static int marker_set_format(struct marker_entry **entry, const char *format)
        e->multi = (*entry)->multi;
        e->ptype = (*entry)->ptype;
        e->refcount = (*entry)->refcount;
-       e->rcu_pending = 0;
        hlist_add_before(&e->hlist, &(*entry)->hlist);
        hlist_del(&(*entry)->hlist);
-       /* Make sure the call_rcu has been executed */
-       if ((*entry)->rcu_pending)
-               rcu_barrier_sched();
        kfree(*entry);
        *entry = e;
        trace_mark(core_marker_format, "name %s format %s",
@@ -658,12 +637,6 @@ int marker_probe_register(const char *name, const char *format,
                        goto end;
                }
        }
-       /*
-        * If we detect that a call_rcu is pending for this marker,
-        * make sure it's executed now.
-        */
-       if (entry->rcu_pending)
-               rcu_barrier_sched();
        old = marker_entry_add_probe(entry, probe, probe_private);
        if (IS_ERR(old)) {
                ret = PTR_ERR(old);
@@ -671,14 +644,11 @@ int marker_probe_register(const char *name, const char *format,
        }
        mutex_unlock(&markers_mutex);
        marker_update_probes();         /* may update entry */
+       synchronize_sched();
+       kfree(old);
        mutex_lock(&markers_mutex);
        entry = get_marker(name);
        WARN_ON(!entry);
-       entry->oldptr = old;
-       entry->rcu_pending = 1;
-       /* write rcu_pending before calling the RCU callback */
-       smp_wmb();
-       call_rcu_sched(&entry->rcu, free_old_closure);
 end:
        mutex_unlock(&markers_mutex);
        return ret;
@@ -708,20 +678,15 @@ int marker_probe_unregister(const char *name,
        entry = get_marker(name);
        if (!entry)
                goto end;
-       if (entry->rcu_pending)
-               rcu_barrier_sched();
        old = marker_entry_remove_probe(entry, probe, probe_private);
        mutex_unlock(&markers_mutex);
        marker_update_probes();         /* may update entry */
+       synchronize_sched();
+       kfree(old);
        mutex_lock(&markers_mutex);
        entry = get_marker(name);
        if (!entry)
                goto end;
-       entry->oldptr = old;
-       entry->rcu_pending = 1;
-       /* write rcu_pending before calling the RCU callback */
-       smp_wmb();
-       call_rcu_sched(&entry->rcu, free_old_closure);
        remove_marker(name);    /* Ignore busy error message */
        ret = 0;
 end:
@@ -787,19 +752,14 @@ int marker_probe_unregister_private_data(marker_probe_func *probe,
                ret = -ENOENT;
                goto end;
        }
-       if (entry->rcu_pending)
-               rcu_barrier_sched();
        old = marker_entry_remove_probe(entry, NULL, probe_private);
        mutex_unlock(&markers_mutex);
        marker_update_probes();         /* may update entry */
+       synchronize_sched();
+       kfree(old);
        mutex_lock(&markers_mutex);
        entry = get_marker_from_private_data(probe, probe_private);
        WARN_ON(!entry);
-       entry->oldptr = old;
-       entry->rcu_pending = 1;
-       /* write rcu_pending before calling the RCU callback */
-       smp_wmb();
-       call_rcu_sched(&entry->rcu, free_old_closure);
        remove_marker(entry->name);     /* Ignore busy error message */
 end:
        mutex_unlock(&markers_mutex);