On Wed, Aug 05, 2015 at 11:51:24AM +0200, mhocko@kernel.org wrote:

From: Michal Hocko <mhocko@suse.com>

alloc_btrfs_bio is relying on GFP_NOFS to allocate a bio but since "mm:
page_alloc: do not lock up GFP_NOFS allocations upon OOM" this is
allowed to fail which can lead to
[   37.928625] kernel BUG at fs/btrfs/extent_io.c:4045

This 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>

Reviewed-by: David Sterba <dsterba@suse.com>