WARNING in __cow_file_range_inline (2)

Status: upstream: reported on 2026/08/13 00:09
Subsystems: btrfs
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+90ab2ca74c4ca62b395f@syzkaller.appspotmail.com
First crash: 14d, last: 3d18h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
2968ca36 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ✅ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ WARNING in __cow_file_range_inline (2) 2026/08/09 23:43 2026/08/09 23:43 2026/08/10 00:26 5d63f80b
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [btrfs?] WARNING in __cow_file_range_inline (2) 0 (1) 2026/08/13 00:09
Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING in __cow_file_range_inline btrfs -1 1 329d 325d 0/29 auto-obsoleted due to no activity on 2026/01/05 19:39

Sample crash report:
loop0: detected capacity change from 0 to 32768
BTRFS: device fsid 395ef67a-297e-477c-816d-cd80a5b93e5d devid 1 transid 8 /dev/loop0 (7:0) scanned by syz.0.0 (5312)
BTRFS info (device loop0): first mount of filesystem 395ef67a-297e-477c-816d-cd80a5b93e5d
BTRFS info (device loop0): using sha256 checksum algorithm
BTRFS warning (device loop0): space cache v1 is being deprecated and will be removed in a future release, please use -o space_cache=v2
BTRFS info (device loop0): rebuilding free space tree
BTRFS info (device loop0): disabling free space tree
BTRFS info (device loop0): clearing compat-ro feature flag for FREE_SPACE_TREE (0x1)
BTRFS info (device loop0): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
BTRFS info (device loop0): enabling ssd optimizations
BTRFS info (device loop0): disabling tree log
BTRFS info (device loop0): enabling disk space caching
BTRFS info (device loop0): force clearing of disk cache
BTRFS info (device loop0): enabling auto defrag
------------[ cut here ]------------
btrfs_abort_should_print_stack(__error)
WARNING: fs/btrfs/inode.c:641 at __cow_file_range_inline+0xef0/0x1000 fs/btrfs/inode.c:641, CPU#0: syz.0.0/5312
Modules linked in:
CPU: 0 UID: 0 PID: 5312 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:__cow_file_range_inline+0xef0/0x1000 fs/btrfs/inode.c:641
Code: e2 74 39 41 83 fd fb 74 3a 41 83 fd f4 75 3b e8 56 36 b2 fd eb 3d e8 4f 36 b2 fd eb 10 e8 48 36 b2 fd eb 09 e8 41 36 b2 fd 90 <0f> 0b 90 44 89 e9 f7 d9 4c 8b 7c 24 18 e9 d4 fd ff ff e8 29 36 b2
RSP: 0018:ffffc9000eeae920 EFLAGS: 00010293
RAX: ffffffff8414df1f RBX: 1ffff92001dd5d34 RCX: ffff88803446cb00
RDX: 0000000000000000 RSI: ffffffff8f1c8350 RDI: 00000000ffffffe4
RBP: ffffc9000eeaeb10 R08: ffff88803446cb00 R09: 0000000000000003
R10: 00000000fffffffb R11: 0000000000000000 R12: dffffc0000000000
R13: 00000000ffffffe4 R14: ffff88804fbb4001 R15: ffff88801ad9d9a0
FS:  00007effaca346c0(0000) GS:ffff88808c533000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000005140 CR3: 0000000012106000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 run_delalloc_inline fs/btrfs/inode.c:2351 [inline]
 btrfs_run_delalloc_range+0x1a84/0x1fd0 fs/btrfs/inode.c:2407
 writepage_delalloc+0x10a4/0x1c60 fs/btrfs/extent_io.c:1671
 extent_writepage fs/btrfs/extent_io.c:2043 [inline]
 extent_write_cache_pages fs/btrfs/extent_io.c:2706 [inline]
 btrfs_writepages+0x1667/0x28b0 fs/btrfs/extent_io.c:2838
 do_writepages+0x338/0x560 mm/page-writeback.c:2571
 filemap_writeback mm/filemap.c:387 [inline]
 filemap_fdatawrite_range+0x1ef/0x2f0 mm/filemap.c:412
 btrfs_fdatawrite_range fs/btrfs/file.c:3884 [inline]
 start_ordered_ops fs/btrfs/file.c:1507 [inline]
 btrfs_sync_file+0x3d0/0x1400 fs/btrfs/file.c:1589
 generic_write_sync include/linux/fs.h:2672 [inline]
 btrfs_do_write_iter+0x640/0x790 fs/btrfs/file.c:1459
 iter_file_splice_write+0xa31/0x1240 fs/splice.c:736
 do_splice_from fs/splice.c:936 [inline]
 direct_splice_actor+0x101/0x160 fs/splice.c:1159
 splice_direct_to_actor+0x57b/0xcb0 fs/splice.c:1103
 do_splice_direct_actor fs/splice.c:1202 [inline]
 do_splice_direct+0x195/0x290 fs/splice.c:1228
 do_sendfile+0x52e/0x7c0 fs/read_write.c:1371
 __do_sys_sendfile64 fs/read_write.c:1432 [inline]
 __se_sys_sendfile64+0x144/0x1a0 fs/read_write.c:1418
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7effabb9e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007effaca33fe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007effabe25fa0 RCX: 00007effabb9e0d9
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000004
RBP: 00007effabc35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0001000000201005 R11: 0000000000000246 R12: 0000000000000000
R13: 00007effabe26038 R14: 00007effabe25fa0 R15: 00007ffc900c7608
 </TASK>

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/19 19:26 upstream bd5f485f3f02 1e72964b .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in __cow_file_range_inline
2026/08/19 19:09 upstream bd5f485f3f02 1e72964b .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in __cow_file_range_inline
2026/08/19 19:08 upstream bd5f485f3f02 1e72964b .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in __cow_file_range_inline
2026/08/08 21:20 upstream a59f57e2aa12 5d63f80b .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in __cow_file_range_inline
* Struck through repros no longer work on HEAD.