btrfs: use __GFP_NOFAIL in alloc_btrfs_bio

alloc_btrfs_bio relies on GFP_NOFS allocation when committing the
transaction but this allocation context is rather weak wrt. reclaim
capabilities. The page allocator currently tries hard to not fail these
allocations if they are small (<=PAGE_ALLOC_COSTLY_ORDER) but it can
still fail if the _current_ process is the OOM killer victim. Moreover
there is an attempt to move away from the default no-fail behavior and
allow these allocation to fail more eagerly. This would lead to:

[   37.928625] kernel BUG at fs/btrfs/extent_io.c:4045

which is clearly undesirable and the nofail behavior should be explicit
if the allocation failure cannot be tolerated.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 7c84a8122c37847c0c0ccb6cfb9818954db1e1df..53a38075911e142ba867a638eb53991b25162a5c 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5082,9 +5082,7 @@ static struct btrfs_bio *alloc_btrfs_bio(int total_stripes, int real_stripes)
                 * and the stripes
                 */
                sizeof(u64) * (total_stripes),
-               GFP_NOFS);
-       if (!bbio)
-               return NULL;
+               GFP_NOFS|__GFP_NOFAIL);
 
        atomic_set(&bbio->error, 0);
        atomic_set(&bbio->refs, 1);