[PATCH 4.20 095/145] btrfs: skip file_extent generation check for free_space_inode in run_delalloc_nocow

From: Greg Kroah-Hartman
Date: Mon Jan 07 2019 - 07:44:24 EST

4.20-stable review patch. If anyone has any objections, please let me know.


From: Lu Fengqi <lufq.fnst@xxxxxxxxxxxxxx>

commit 27a7ff554e8d349627a90bda275c527b7348adae upstream.

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: stable@xxxxxxxxxxxxxxx # 4.18+
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Lu Fengqi <lufq.fnst@xxxxxxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/btrfs/inode.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1372,7 +1372,8 @@ 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)