[PATCH] kdump: export per cpu crash notes pointer through sysfs

- Kexec on panic functionality allocates memory for saving cpu registers in
  case of system crash event.  Address of this allocated memory needs to be
  exported to user space, which is used by kexec-tools.

- Previously, a single /sys/kernel/crash_notes entry was being exported as
  memory allocated was a single continuous array.  Now memory allocation being
  dyanmic and per cpu based, address of per cpu buffer is exported through
  "/sys/devices/system/cpu/cpuX/crash_notes"

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 281d26784d251107bc6b158ba3ce5f5904a157fd..982e6583cd633a533fe8a7dbdfe30edc3cbd5437 100644 (file)
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -83,6 +83,33 @@ static inline void register_cpu_control(struct cpu *cpu)
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
+#ifdef CONFIG_KEXEC
+#include <linux/kexec.h>
+
+static ssize_t show_crash_notes(struct sys_device *dev, char *buf)
+{
+       struct cpu *cpu = container_of(dev, struct cpu, sysdev);
+       ssize_t rc;
+       unsigned long long addr;
+       int cpunum;
+
+       cpunum = cpu->sysdev.id;
+
+       /*
+        * Might be reading other cpu's data based on which cpu read thread
+        * has been scheduled. But cpu data (memory) is allocated once during
+        * boot up and this data does not change there after. Hence this
+        * operation should be safe. No locking required.
+        */
+       get_cpu();
+       addr = __pa(per_cpu_ptr(crash_notes, cpunum));
+       rc = sprintf(buf, "%Lx\n", addr);
+       put_cpu();
+       return rc;
+}
+static SYSDEV_ATTR(crash_notes, 0400, show_crash_notes, NULL);
+#endif
+
 /*
  * register_cpu - Setup a driverfs device for a CPU.
  * @cpu - Callers can set the cpu->no_control field to 1, to indicate not to
@@ -108,6 +135,11 @@ int __devinit register_cpu(struct cpu *cpu, int num, struct node *root)
                register_cpu_control(cpu);
        if (!error)
                cpu_sys_devices[num] = &cpu->sysdev;
+
+#ifdef CONFIG_KEXEC
+       if (!error)
+               error = sysdev_create_file(&cpu->sysdev, &attr_crash_notes);
+#endif
        return error;
 }
 

diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 99af8b05eeaa754de098195a7299bff216040180..d5eeae0fa5bc5c6de327a7c0f583c4fdaca16b50 100644 (file)
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -51,16 +51,6 @@ static ssize_t uevent_helper_store(struct subsystem *subsys, const char *page, s
 KERNEL_ATTR_RW(uevent_helper);
 #endif
 
-#ifdef CONFIG_KEXEC
-#include <asm/kexec.h>
-
-static ssize_t crash_notes_show(struct subsystem *subsys, char *page)
-{
-       return sprintf(page, "%p\n", (void *)crash_notes);
-}
-KERNEL_ATTR_RO(crash_notes);
-#endif
-
 decl_subsys(kernel, NULL, NULL);
 EXPORT_SYMBOL_GPL(kernel_subsys);
 
@@ -68,9 +58,6 @@ static struct attribute * kernel_attrs[] = {
 #ifdef CONFIG_HOTPLUG
        &uevent_seqnum_attr.attr,
        &uevent_helper_attr.attr,
-#endif
-#ifdef CONFIG_KEXEC
-       &crash_notes_attr.attr,
 #endif
        NULL
 };