md/bitmap: prevent bitmap_daemon_work running while initialising bitmap

commit afbaa90b80b1ec66e5137cc3824746bfdf559b18 upstream.

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.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 703a3fa831b..2eba9a12a6a 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1897,7 +1897,9 @@ int bitmap_load(mddev_t *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;