md/bitmap: prevent bitmap_daemon_work running while initialising bitmap

If a bitmap is added while the array is active, it is possible
for bitmap_daemon_work to run while the bitmap is being
initialised.
This is particularly a problem if bitmap_daemon_work sees
bitmap->filemap as non-NULL before it has been filled in properly.
So hold bitmap_info.mutex while filling in ->filemap
to prevent problems.

This patch is suitable for any -stable kernel, though it might not
apply cleanly before about 3.1.

Cc: stable@vger.kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 1c264a701e70..97e73e555d11 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1785,7 +1785,9 @@ int bitmap_load(struct mddev *mddev)
                  * re-add of a missing device */
                 start = mddev->recovery_cp;
 
+        mutex_lock(&mddev->bitmap_info.mutex);
         err = bitmap_init_from_disk(bitmap, start);
+        mutex_unlock(&mddev->bitmap_info.mutex);
 
         if (err)
                 goto out;