[PATCH] md: Improve locking around error handling

The error handling routines don't use proper locking, and so two concurrent
errors could trigger a problem.

So:
  - use test-and-set and test-and-clear to synchonise
    the In_sync bits with the ->degraded count
  - use the spinlock to protect updates to the
    degraded count (could use an atomic_t but that
    would be a bigger change in code, and isn't
    really justified)
  - remove un-necessary locking in raid5

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 233a4faede94..64f8016ab740 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -950,14 +950,16 @@ static void error(mddev_t *mddev, mdk_rdev_t *rdev)
                  * really dead" tests...
                  */
                 return;
-        if (test_bit(In_sync, &rdev->flags)) {
+        if (test_and_clear_bit(In_sync, &rdev->flags)) {
+                unsigned long flags;
+                spin_lock_irqsave(&conf->device_lock, flags);
                 mddev->degraded++;
+                spin_unlock_irqrestore(&conf->device_lock, flags);
                 /*
                  * if recovery is running, make sure it aborts.
                  */
                 set_bit(MD_RECOVERY_ERR, &mddev->recovery);
         }
-        clear_bit(In_sync, &rdev->flags);
         set_bit(Faulty, &rdev->flags);
         set_bit(MD_CHANGE_DEVS, &mddev->flags);
         printk(KERN_ALERT "raid10: Disk failure on %s, disabling device. \n"
@@ -1033,9 +1035,11 @@ static int raid10_spare_active(mddev_t *mddev)
                 tmp = conf->mirrors + i;
                 if (tmp->rdev
                     && !test_bit(Faulty, &tmp->rdev->flags)
-                    && !test_bit(In_sync, &tmp->rdev->flags)) {
+                    && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
+                        unsigned long flags;
+                        spin_lock_irqsave(&conf->device_lock, flags);
                         mddev->degraded--;
-                        set_bit(In_sync, &tmp->rdev->flags);
+                        spin_unlock_irqrestore(&conf->device_lock, flags);
                 }
         }