[PATCH] md: fix potential memalloc deadlock in md

If a GFP_KERNEL allocation is attempted in md while the mddev_lock is held,
it is possible for a deadlock to eventuate.

This happens if the array was marked 'clean', and the memalloc triggers a
write-out to the md device.

For the writeout to succeed, the array must be marked 'dirty', and that
requires getting the mddev_lock.

So, before attempting a GFP_KERNEL allocation while holding the lock, make
sure the array is marked 'dirty' (unless it is currently read-only).

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

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index be008f034ada..8a30b297ac3a 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -405,6 +405,8 @@ static int resize_stripes(raid5_conf_t *conf, int newsize)
         if (newsize <= conf->pool_size)
                 return 0; /* never bother to shrink */
 
+        md_allow_write(conf->mddev);
+
         /* Step 1 */
         sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
                                sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
@@ -3250,6 +3252,7 @@ raid5_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len)
                 else
                         break;
         }
+        md_allow_write(mddev);
         while (new > conf->max_nr_stripes) {
                 if (grow_one_stripe(conf))
                         conf->max_nr_stripes++;