[PATCH] md: ensure bitmap_writeback_daemon handles shutdown properly.

mddev->bitmap gets clearred before the writeback daemon is stopped.  So the
write_back daemon needs to be careful not to dereference the 'bitmap' if it is
NULL.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 90fe70d76a31..87145faac491 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1156,6 +1156,9 @@ static void bitmap_writeback_daemon(mddev_t *mddev)
                 err = -EINTR;
                 goto out;
         }
+        if (bitmap == NULL)
+                /* about to be stopped. */
+                return;
 
         PRINTK("%s: bitmap writeback daemon woke up...\n", bmname(bitmap));
         /* wait on bitmap page writebacks */