[PATCH v2] btrfs: volumes: Check memory allocation failure for alloc_btrfs_bio()

[PATCH v2] btrfs: volumes: Check memory allocation failure for alloc_btrfs_bio()

[Qu Wenruo]

[BUG]
With kmalloc failure injection for submit_one_bio(), btrfs can crash like:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
  #PF error: [WRITE]
  PGD 0 P4D 0
  Oops: 0002 [#1] PREEMPT SMP PTI
  CPU: 1 PID: 247 Comm: kworker/u8:4 Not tainted 5.1.0-rc5-custom+ #19
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  Workqueue: writeback wb_workfn (flush-btrfs-6)
  RIP: 0010:alloc_btrfs_bio+0x1e/0x30 [btrfs]
  Call Trace:
   __btrfs_map_block+0x5ce/0x1210 [btrfs]
   ? btrfs_bio_counter_inc_blocked+0x3a/0xc0 [btrfs]
   btrfs_map_bio+0x9a/0x430 [btrfs]
   btree_submit_bio_hook+0x82/0xb0 [btrfs]
   submit_one_bio+0x95/0xc0 [btrfs]
   copy_oldmem_page_encrypted+0x20/0x20
   ? write_one_eb+0x18f/0x2a0 [btrfs]
   ? end_extent_buffer_writeback+0x20/0x20 [btrfs]
   ? btree_write_cache_pages+0x12c/0x350 [btrfs]
   ? do_writepages+0x41/0xd0
   ? __writeback_single_inode+0x54/0x650
   ? writeback_sb_inodes+0x1f9/0x540
   ? __writeback_inodes_wb+0x5d/0xb0
   ? wb_writeback+0x340/0x4b0
   ? wb_workfn+0x410/0x5d0
   ? process_one_work+0x294/0x650
   ? worker_thread+0x2d/0x3d0
   ? process_one_work+0x650/0x650
   ? kthread+0x112/0x130
   ? kthread_park+0x80/0x80
   ? ret_from_fork+0x3a/0x50
  ---[ end trace b637169fb8b17c9c ]---

[CAUSE]
The kmalloc() call in alloc_btrfs_bio() has __GFP_NOFAIL flag set, so we
don't check the returned pointer.
However all alloc_btrfs_bio() callers have checked NULL pointer, thus
even we kmalloc() failed, we won't panic anyway.

[FIX]
Remove the __GFP_NOFAIL flag and check the returned pointer from
kmalloc().

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
---
Changelog:
- Remove the __GFP_NOFAIL flag
  Especially when all callers are handling memory allocation failure,
  there is no need for __GFP_NOFAIL.
---
 fs/btrfs/volumes.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 78bab7803bda..7e1ad6dd672e 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5580,8 +5580,10 @@ static struct btrfs_bio *alloc_btrfs_bio(int total_stripes, int real_stripes)
 		 * and the stripes
 		 */
 		sizeof(u64) * (total_stripes),
-		GFP_NOFS|__GFP_NOFAIL);
+		GFP_NOFS);
 
+	if (!bbio)
+		return NULL;
 	atomic_set(&bbio->error, 0);
 	refcount_set(&bbio->refs, 1);
 
-- 
2.21.0