btrfs: skip file_extent generation check for free_space_inode in run_delalloc_nocow
authorLu Fengqi <>
Thu, 29 Nov 2018 09:31:32 +0000 (17:31 +0800)
committerDavid Sterba <>
Mon, 17 Dec 2018 13:51:44 +0000 (14:51 +0100)
The test case btrfs/001 with inode_cache mount option will encounter the
following warning:

  WARNING: CPU: 1 PID: 23700 at fs/btrfs/inode.c:956 cow_file_range.isra.19+0x32b/0x430 [btrfs]
  CPU: 1 PID: 23700 Comm: btrfs Kdump: loaded Tainted: G        W  O      4.20.0-rc4-custom+ #30
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:cow_file_range.isra.19+0x32b/0x430 [btrfs]
  Call Trace:
   ? free_extent_buffer+0x46/0x90 [btrfs]
   run_delalloc_nocow+0x455/0x900 [btrfs]
   btrfs_run_delalloc_range+0x1a7/0x360 [btrfs]
   writepage_delalloc+0xf9/0x150 [btrfs]
   __extent_writepage+0x125/0x3e0 [btrfs]
   extent_write_cache_pages+0x1b6/0x3e0 [btrfs]
   ? __wake_up_common_lock+0x63/0xc0
   extent_writepages+0x50/0x80 [btrfs]
   ? __filemap_fdatawrite_range+0x9e/0xf0
   btrfs_fdatawrite_range+0x1b/0x50 [btrfs]
   __btrfs_write_out_cache+0x42c/0x480 [btrfs]
   btrfs_write_out_ino_cache+0x84/0xd0 [btrfs]
   btrfs_save_ino_cache+0x551/0x660 [btrfs]
   commit_fs_roots+0xc5/0x190 [btrfs]
   btrfs_commit_transaction+0x2bf/0x8d0 [btrfs]
   btrfs_mksubvol+0x48d/0x4d0 [btrfs]
   btrfs_ioctl_snap_create_transid+0x170/0x180 [btrfs]
   btrfs_ioctl_snap_create_v2+0x124/0x180 [btrfs]
   btrfs_ioctl+0x123f/0x3030 [btrfs]

The file extent generation of the free space inode is equal to the last
snapshot of the file root, so the inode will be passed to cow_file_rage.
But the inode was created and its extents were preallocated in
btrfs_save_ino_cache, there are no cow copies on disk.

The preallocated extent is not yet in the extent tree, and
btrfs_cross_ref_exist will ignore the -ENOENT returned by
check_committed_ref, so we can directly write the inode to the disk.

Fixes: 78d4295b1eee ("btrfs: lift some btrfs_cross_ref_exist checks in nocow path")
CC: # 4.18+
Reviewed-by: Filipe Manana <>
Signed-off-by: Lu Fengqi <>
Signed-off-by: David Sterba <>

index b4129d9072eccb27595c61af31a26607f1e0f400..e7b97c699acf6e20515f1fe430b649020b09cc94 100644 (file)
@@ -1369,7 +1369,8 @@ next_slot:
                         * Do the same check as in btrfs_cross_ref_exist but
                         * without the unnecessary search.
-                       if (btrfs_file_extent_generation(leaf, fi) <=
+                       if (!nolock &&
+                           btrfs_file_extent_generation(leaf, fi) <=
                                goto out_check;
                        if (extent_type == BTRFS_FILE_EXTENT_REG && !force)