[PATCH] md: fix deadlock due to md thread processing delayed requests.

Before completing a 'write' the md superblock might need to be updated.
This is best done by the md_thread.

The current code schedules this up and queues the write request for later
handling by the md_thread.

However some personalities (Raid5/raid6) will deadlock if the md_thread
tries to submit requests to its own array.

So this patch changes things so the processes submitting the request waits
for the superblock to be written and then submits the request itself.

This fixes a recently-created deadlock in raid5/raid6

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, 1 insertions, 1 deletions

diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 6cdcb4434c6c..3e977025cf43 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -261,7 +261,7 @@ struct mddev_s
         sector_t                        recovery_cp;
 
         spinlock_t                      write_lock;
-        struct bio_list                 write_list;
+        wait_queue_head_t               sb_wait;        /* for waiting on superblock updates */
 
         unsigned int                    safemode;       /* if set, update "clean" superblock
                                                          * when no writes pending.