WARNING in btrfs_add_reserved_bytes (2)

Status: upstream: reported C repro on 2026/09/26 22:23
Subsystems: btrfs
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+9f330950ca662bc43bf0@syzkaller.appspotmail.com
First crash: 1d12h, last: 1d12h
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
de128c3d assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ✅ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ WARNING in btrfs_add_reserved_bytes (2) 2026/09/25 17:06 2026/09/25 17:06 2026/09/25 17:50 f281d9d2
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [btrfs?] WARNING in btrfs_add_reserved_bytes (2) 0 (1) 2026/09/26 22:23
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream WARNING in btrfs_add_reserved_bytes btrfs -1 1 1101d 1097d 0/29 auto-obsoleted due to no activity on 2023/12/30 18:41

Sample crash report:
------------[ cut here ]------------
1
WARNING: fs/btrfs/space-info.h:286 at btrfs_space_info_update_bytes_may_use fs/btrfs/space-info.h:286 [inline], CPU#0: syz-executor/5443
WARNING: fs/btrfs/space-info.h:286 at btrfs_add_reserved_bytes+0x51b/0x8b0 fs/btrfs/block-group.c:4029, CPU#0: syz-executor/5443
Modules linked in:
CPU: 0 UID: 0 PID: 5443 Comm: syz-executor 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:btrfs_space_info_update_bytes_may_use fs/btrfs/space-info.h:286 [inline]
RIP: 0010:btrfs_add_reserved_bytes+0x51b/0x8b0 fs/btrfs/block-group.c:4029
Code: ac 24 80 00 00 00 74 08 48 89 ef e8 2f b4 f6 fd 4c 8b 75 00 4c 89 f7 4c 89 ee e8 30 14 85 fd 4d 39 ee 73 18 e8 56 11 85 fd 90 <0f> 0b 90 45 31 f6 eb 2e e8 48 11 85 fd e9 f8 fb ff ff e8 3e 11 85
RSP: 0018:ffffc90001e1ec10 EFLAGS: 00010293
RAX: ffffffff8442dbba RBX: 1ffff1100889b910 RCX: ffff888000bc4b00
RDX: 0000000000000000 RSI: 0000000000001000 RDI: 0000000000000000
RBP: ffff8880444dc880 R08: ffffffff907a847f R09: 1ffffffff20f508f
R10: dffffc0000000000 R11: fffffbfff20f5090 R12: ffff8880444dc800
R13: 0000000000001000 R14: 0000000000000000 R15: ffff8880444dc820
FS:  000055559168c500(0000) GS:ffff88808c2bf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005555916a7a28 CR3: 000000001f9a3000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 find_free_extent+0x3ff4/0x5cd0 fs/btrfs/extent-tree.c:4776
 btrfs_reserve_extent+0x349/0x850 fs/btrfs/extent-tree.c:4904
 btrfs_alloc_tree_block+0x1ed/0x1160 fs/btrfs/extent-tree.c:5375
 btrfs_force_cow_block+0x562/0x1bf0 fs/btrfs/ctree.c:501
 btrfs_cow_block+0x3f1/0xaf0 fs/btrfs/ctree.c:696
 btrfs_search_slot+0xd70/0x2d20 fs/btrfs/ctree.c:-1
 btrfs_insert_empty_items+0xa3/0x1a0 fs/btrfs/ctree.c:4310
 btrfs_insert_delayed_item fs/btrfs/delayed-inode.c:755 [inline]
 btrfs_insert_delayed_items fs/btrfs/delayed-inode.c:832 [inline]
 __btrfs_commit_inode_delayed_items+0xb0e/0x1ec0 fs/btrfs/delayed-inode.c:1115
 __btrfs_run_delayed_items+0x1d0/0x420 fs/btrfs/delayed-inode.c:1158
 btrfs_commit_transaction+0x844/0x3170 fs/btrfs/transaction.c:2383
 sync_filesystem+0x1d2/0x240 fs/sync.c:66
 generic_shutdown_super+0x77/0x2d0 fs/super.c:734
 kill_anon_super+0x3b/0x70 fs/super.c:1356
 btrfs_kill_super+0x41/0x50 fs/btrfs/super.c:2152
 deactivate_locked_super+0xbc/0x110 fs/super.c:589
 cleanup_mnt+0x3d3/0x460 fs/namespace.c:1317
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:70 [inline]
 exit_to_user_mode_loop+0x204/0x770 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:343 [inline]
 do_syscall_64+0x328/0x520 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f68fe39f397
Code: a2 c7 05 5c 43 25 00 00 00 00 00 eb 96 e8 e1 12 00 00 90 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007fffcd75c7e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007f68fe4344bb RCX: 00007f68fe39f397
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007fffcd75c8a0
RBP: 00007fffcd75c8a0 R08: 00007fffcd75d8a0 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fffcd75d930
R13: 00007f68fe4344bb R14: 000000000006482c R15: 00007fffcd75d970
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/25 17:06 upstream 165768bb7026 f281d9d2 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci-snapshot-upstream-root WARNING in btrfs_add_reserved_bytes
* Struck through repros no longer work on HEAD.