possible deadlock in btrfs_start_transaction (2)

Status: upstream: reported C repro on 2025/02/02 07:03
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+b56327bfdb9a4b46222a@syzkaller.appspotmail.com
First crash: 562d, last: 31d
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2025/03/20 upstream (ToT) a7f2e10ecd8f C [report] BUG: MAX_LOCKDEP_KEYS too low!
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 possible deadlock in btrfs_start_transaction 4 2 715d 754d 0/3 auto-obsoleted due to no activity on 2024/12/10 18:05
▶ ▼ Last patch testing requests (10)
Created Duration User Patch Repo Result
2026/07/17 17:58 17m retest repro linux-5.15.y report log
2026/07/17 17:58 19m retest repro linux-5.15.y report log
2026/07/17 17:58 16m retest repro linux-5.15.y report log
2026/07/17 17:58 16m retest repro linux-5.15.y report log
2026/06/24 08:12 16m retest repro linux-5.15.y report log
2026/06/05 08:18 18m retest repro linux-5.15.y report log
2026/04/15 09:59 15m retest repro linux-5.15.y report log
2026/04/15 09:59 14m retest repro linux-5.15.y report log
2026/04/15 09:59 18m retest repro linux-5.15.y report log
2026/04/15 09:59 11m retest repro linux-5.15.y report log

Sample crash report:
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)
======================================================
WARNING: possible circular locking dependency detected
5.15.178-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor241/4019 is trying to acquire lock:
ffff0000d3974650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:777

but task is already holding lock:
ffff0000dbfa8610 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: inode_lock include/linux/fs.h:789 [inline]
ffff0000dbfa8610 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: vfs_fileattr_set+0x110/0xad4 fs/ioctl.c:685

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&type->i_mutex_dir_key#6){++++}-{3:3}:
       down_read+0xc0/0x398 kernel/locking/rwsem.c:1498
       inode_lock_shared include/linux/fs.h:799 [inline]
       lookup_slow+0x50/0x84 fs/namei.c:1679
       walk_component+0x394/0x4cc fs/namei.c:1976
       lookup_last fs/namei.c:2431 [inline]
       path_lookupat+0x13c/0x3d0 fs/namei.c:2455
       filename_lookup+0x1c4/0x4c8 fs/namei.c:2484
       kern_path+0x4c/0x194 fs/namei.c:2582
       lookup_bdev+0xc0/0x25c block/bdev.c:979
       device_matched fs/btrfs/volumes.c:568 [inline]
       btrfs_free_stale_devices+0x658/0x9ec fs/btrfs/volumes.c:608
       btrfs_forget_devices+0x5c/0x98 fs/btrfs/volumes.c:1431
       btrfs_control_ioctl+0x12c/0x248 fs/btrfs/super.c:2451
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl fs/ioctl.c:860 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #2 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x194/0x2154 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0xa4/0xf8 kernel/locking/mutex.c:743
       btrfs_run_dev_stats+0xe4/0xe24 fs/btrfs/volumes.c:7985
       commit_cowonly_roots+0x17c/0x808 fs/btrfs/transaction.c:1290
       btrfs_commit_transaction+0xef4/0x30f0 fs/btrfs/transaction.c:2392
       btrfs_clear_free_space_tree+0x5d0/0x9bc fs/btrfs/free-space-tree.c:1264
       btrfs_start_pre_rw_mount+0x24c/0x578 fs/btrfs/disk-io.c:3079
       open_ctree+0x2290/0x28f4 fs/btrfs/disk-io.c:3634
       btrfs_fill_super+0x1b4/0x2c8 fs/btrfs/super.c:1387
       btrfs_mount_root+0x6f8/0x7f8 fs/btrfs/super.c:1752
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
       vfs_get_tree+0x90/0x274 fs/super.c:1530
       fc_mount fs/namespace.c:1000 [inline]
       vfs_kern_mount+0xdc/0x178 fs/namespace.c:1030
       btrfs_mount+0x328/0x9b8 fs/btrfs/super.c:1812
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
       vfs_get_tree+0x90/0x274 fs/super.c:1530
       do_new_mount+0x278/0x8fc fs/namespace.c:3012
       path_mount+0x594/0x101c fs/namespace.c:3342
       do_mount fs/namespace.c:3355 [inline]
       __do_sys_mount fs/namespace.c:3563 [inline]
       __se_sys_mount fs/namespace.c:3540 [inline]
       __arm64_sys_mount+0x510/0x5e0 fs/namespace.c:3540
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #1 (&fs_info->tree_log_mutex){+.+.}-{3:3}:
       __lock_release kernel/locking/lockdep.c:5339 [inline]
       lock_release+0x340/0xa1c kernel/locking/lockdep.c:5643
       __mutex_unlock_slowpath+0xe0/0x6d4 kernel/locking/mutex.c:851
       mutex_unlock+0x8c/0xe0 kernel/locking/mutex.c:536
       btrfs_commit_transaction+0x1650/0x30f0 fs/btrfs/transaction.c:2439
       btrfs_clear_free_space_tree+0x5d0/0x9bc fs/btrfs/free-space-tree.c:1264
       btrfs_start_pre_rw_mount+0x24c/0x578 fs/btrfs/disk-io.c:3079
       open_ctree+0x2290/0x28f4 fs/btrfs/disk-io.c:3634
       btrfs_fill_super+0x1b4/0x2c8 fs/btrfs/super.c:1387
       btrfs_mount_root+0x6f8/0x7f8 fs/btrfs/super.c:1752
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
       vfs_get_tree+0x90/0x274 fs/super.c:1530
       fc_mount fs/namespace.c:1000 [inline]
       vfs_kern_mount+0xdc/0x178 fs/namespace.c:1030
       btrfs_mount+0x328/0x9b8 fs/btrfs/super.c:1812
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:611
       vfs_get_tree+0x90/0x274 fs/super.c:1530
       do_new_mount+0x278/0x8fc fs/namespace.c:3012
       path_mount+0x594/0x101c fs/namespace.c:3342
       do_mount fs/namespace.c:3355 [inline]
       __do_sys_mount fs/namespace.c:3563 [inline]
       __se_sys_mount fs/namespace.c:3540 [inline]
       __arm64_sys_mount+0x510/0x5e0 fs/namespace.c:3540
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #0 (sb_internal#2){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x32d4/0x7638 kernel/locking/lockdep.c:5012
       lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1813 [inline]
       sb_start_intwrite include/linux/fs.h:1930 [inline]
       start_transaction+0x644/0x1480 fs/btrfs/transaction.c:678
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:777
       btrfs_fileattr_set+0x4dc/0x9b8 fs/btrfs/ioctl.c:331
       vfs_fileattr_set+0x70c/0xad4 fs/ioctl.c:700
       do_vfs_ioctl+0x1634/0x2a38
       __do_sys_ioctl fs/ioctl.c:872 [inline]
       __se_sys_ioctl fs/ioctl.c:860 [inline]
       __arm64_sys_ioctl+0xe4/0x1c8 fs/ioctl.c:860
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

other info that might help us debug this:

Chain exists of:
  sb_internal#2 --> &fs_devs->device_list_mutex --> &type->i_mutex_dir_key#6

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&type->i_mutex_dir_key#6);
                               lock(&fs_devs->device_list_mutex);
                               lock(&type->i_mutex_dir_key#6);
  lock(sb_internal#2);

 *** DEADLOCK ***

2 locks held by syz-executor241/4019:
 #0: ffff0000d3974460 (sb_writers#8){.+.+}-{0:0}, at: mnt_want_write_file+0x64/0x1e8 fs/namespace.c:421
 #1: ffff0000dbfa8610 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: inode_lock include/linux/fs.h:789 [inline]
 #1: ffff0000dbfa8610 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: vfs_fileattr_set+0x110/0xad4 fs/ioctl.c:685

stack backtrace:
CPU: 1 PID: 4019 Comm: syz-executor241 Not tainted 5.15.178-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call trace:
 dump_backtrace+0x0/0x530 arch/arm64/kernel/stacktrace.c:152
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
 dump_stack+0x1c/0x58 lib/dump_stack.c:113
 print_circular_bug+0x150/0x1b8 kernel/locking/lockdep.c:2011
 check_noncircular+0x2cc/0x378 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x32d4/0x7638 kernel/locking/lockdep.c:5012
 lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
 percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
 __sb_start_write include/linux/fs.h:1813 [inline]
 sb_start_intwrite include/linux/fs.h:1930 [inline]
 start_transaction+0x644/0x1480 fs/btrfs/transaction.c:678
 btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:777
 btrfs_fileattr_set+0x4dc/0x9b8 fs/btrfs/ioctl.c:331
 vfs_fileattr_set+0x70c/0xad4 fs/ioctl.c:700
 do_vfs_ioctl+0x1634/0x2a38
 __do_sys_ioctl fs/ioctl.c:872 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __arm64_sys_ioctl+0xe4/0x1c8 fs/ioctl.c:860
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
 el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
 el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
 el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

Crashes (8):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/02/02 20:26 linux-5.15.y c16c81c81336 568559e4 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-5-15-kasan-arm64 possible deadlock in btrfs_start_transaction
2025/02/02 18:41 linux-5.15.y c16c81c81336 568559e4 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-5-15-kasan-arm64 possible deadlock in btrfs_start_transaction
2025/02/02 16:47 linux-5.15.y c16c81c81336 568559e4 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-5-15-kasan-arm64 possible deadlock in btrfs_start_transaction
2025/02/02 14:28 linux-5.15.y c16c81c81336 568559e4 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-5-15-kasan-arm64 possible deadlock in btrfs_start_transaction
2025/02/02 11:23 linux-5.15.y c16c81c81336 568559e4 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-5-15-kasan-arm64 possible deadlock in btrfs_start_transaction
2025/02/02 09:06 linux-5.15.y c16c81c81336 568559e4 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-linux-5-15-kasan-arm64 possible deadlock in btrfs_start_transaction
2025/05/11 19:39 linux-5.15.y 3b8db0e4f263 77908e5f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in btrfs_start_transaction
2025/02/02 07:03 linux-5.15.y c16c81c81336 568559e4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-arm64 possible deadlock in btrfs_start_transaction
* Struck through repros no longer work on HEAD.