possible deadlock in btrfs_join_transaction (4)

Status: auto-obsoleted due to no activity on 2026/10/12 08:01
Reported-by: syzbot+8d1fbb49d58ce1fcca78@syzkaller.appspotmail.com
First crash: 121d, last: 101d
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in btrfs_join_transaction (2) btrfs 4 11 285d 474d 0/29 auto-obsoleted due to no activity on 2026/04/11 02:59
linux-6.1 possible deadlock in btrfs_join_transaction 4 2 504d 525d 0/3 auto-obsoleted due to no activity on 2025/09/04 19:00
linux-6.1 possible deadlock in btrfs_join_transaction (2) 4 1 366d 366d 0/3 auto-obsoleted due to no activity on 2026/01/20 21:10
upstream possible deadlock in btrfs_join_transaction btrfs 4 syz, C 2 1414d 1419d 0/29 auto-obsoleted due to no activity on 2023/03/29 11:54
linux-6.1 possible deadlock in btrfs_join_transaction (3) 4 2 246d 266d 0/3 auto-obsoleted due to no activity on 2026/05/20 06:23
linux-5.15 possible deadlock in btrfs_join_transaction origin:upstream 4 syz, C error 62 56d 997d 0/3 upstream: reported C repro on 2024/01/20 21:24

Sample crash report:
device ip6tnl1 entered promiscuous mode
netlink: 4 bytes leftover after parsing attributes in process `syz.4.506'.
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.506/8900 is trying to acquire lock:
ffff0000dd202650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781

but task is already holding lock:
ffff0000d5c57348 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
ffff0000d5c57348 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x148/0x298 mm/util.c:518

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (&mm->mmap_lock){++++}-{3:3}:
       __might_fault+0xc4/0x124 mm/memory.c:5850
       filldir64+0x2dc/0x930 fs/readdir.c:335
       dir_emit_dot include/linux/fs.h:3698 [inline]
       dir_emit_dots include/linux/fs.h:3709 [inline]
       dcache_readdir+0x144/0x638 fs/libfs.c:197
       iterate_dir+0x1f0/0x4d0 fs/readdir.c:-1
       __do_sys_getdents64 fs/readdir.c:369 [inline]
       __se_sys_getdents64 fs/readdir.c:354 [inline]
       __arm64_sys_getdents64+0x11c/0x314 fs/readdir.c:354
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #5 (&type->i_mutex_dir_key#2){++++}-{3:3}:
       down_read+0x64/0x300 kernel/locking/rwsem.c:1520
       inode_lock_shared include/linux/fs.h:768 [inline]
       lookup_slow+0x50/0x84 fs/namei.c:1714
       walk_component+0x278/0x374 fs/namei.c:2006
       lookup_last fs/namei.c:2463 [inline]
       path_lookupat+0x168/0x3f0 fs/namei.c:2487
       filename_lookup+0x1d4/0x490 fs/namei.c:2516
       kern_path+0x48/0x6c fs/namei.c:2614
       is_same_device fs/btrfs/volumes.c:695 [inline]
       device_list_add+0x127c/0x1c8c fs/btrfs/volumes.c:928
       btrfs_scan_one_device+0x368/0x558 fs/btrfs/volumes.c:1461
       btrfs_mount_root+0x470/0x7ec fs/btrfs/super.c:1796
       legacy_get_tree+0xd8/0x174 fs/fs_context.c:632
       vfs_get_tree+0x90/0x278 fs/super.c:1573
       fc_mount fs/namespace.c:1048 [inline]
       vfs_kern_mount+0xdc/0x178 fs/namespace.c:1078
       btrfs_mount+0x2dc/0x974 fs/btrfs/super.c:1894
       legacy_get_tree+0xd8/0x174 fs/fs_context.c:632
       vfs_get_tree+0x90/0x278 fs/super.c:1573
       do_new_mount+0x228/0x804 fs/namespace.c:3078
       path_mount+0x5ac/0xe6c fs/namespace.c:3408
       do_mount fs/namespace.c:3421 [inline]
       __do_sys_mount fs/namespace.c:3629 [inline]
       __se_sys_mount fs/namespace.c:3606 [inline]
       __arm64_sys_mount+0x4a0/0x5a0 fs/namespace.c:3606
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #4 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1a0/0x1f3c kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       btrfs_run_dev_stats+0xfc/0xda0 fs/btrfs/volumes.c:8071
       commit_cowonly_roots+0x170/0x718 fs/btrfs/transaction.c:1298
       btrfs_commit_transaction+0x1134/0x28e4 fs/btrfs/transaction.c:2444
       btrfs_sync_fs+0x25c/0xa30 fs/btrfs/super.c:1535
       sync_filesystem+0x1a0/0x218 fs/sync.c:66
       generic_shutdown_super+0x74/0x32c fs/super.c:474
       kill_anon_super+0x4c/0x80 fs/super.c:1128
       btrfs_kill_super+0x44/0x5c fs/btrfs/super.c:2448
       deactivate_locked_super+0xb4/0x128 fs/super.c:332
       deactivate_super+0xe4/0x104 fs/super.c:363
       cleanup_mnt+0x3a8/0x430 fs/namespace.c:1191
       __cleanup_mnt+0x20/0x30 fs/namespace.c:1198
       task_work_run+0x1f4/0x280 kernel/task_work.c:203
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       do_notify_resume+0x20f8/0x2c84 arch/arm64/kernel/signal.c:1151
       prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
       exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
       el0_svc+0x98/0x128 arch/arm64/kernel/entry-common.c:638
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #3 (&fs_info->reloc_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1a0/0x1f3c kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       btrfs_record_root_in_trans fs/btrfs/transaction.c:488 [inline]
       start_transaction+0x42c/0x1040 fs/btrfs/transaction.c:731
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:767
       btrfs_setsize fs/btrfs/inode.c:5273 [inline]
       btrfs_setattr+0x4dc/0xeb4 fs/btrfs/inode.c:5344
       notify_change+0xb5c/0xe20 fs/attr.c:499
       do_truncate+0x188/0x20c fs/open.c:65
       vfs_truncate+0x23c/0x2b0 fs/open.c:111
       do_sys_truncate+0xec/0x1b4 fs/open.c:134
       __do_sys_truncate fs/open.c:146 [inline]
       __se_sys_truncate fs/open.c:144 [inline]
       __arm64_sys_truncate+0x5c/0x70 fs/open.c:144
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x16c/0xb08 fs/btrfs/transaction.c:303
       start_transaction+0x794/0x1040 fs/btrfs/transaction.c:668
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:767
       btrfs_setsize fs/btrfs/inode.c:5273 [inline]
       btrfs_setattr+0x4dc/0xeb4 fs/btrfs/inode.c:5344
       notify_change+0xb5c/0xe20 fs/attr.c:499
       do_truncate+0x188/0x20c fs/open.c:65
       vfs_truncate+0x23c/0x2b0 fs/open.c:111
       do_sys_truncate+0xec/0x1b4 fs/open.c:134
       __do_sys_truncate fs/open.c:146 [inline]
       __se_sys_truncate fs/open.c:144 [inline]
       __arm64_sys_truncate+0x5c/0x70 fs/open.c:144
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x140/0xb08 fs/btrfs/transaction.c:302
       start_transaction+0x794/0x1040 fs/btrfs/transaction.c:668
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:767
       btrfs_setsize fs/btrfs/inode.c:5273 [inline]
       btrfs_setattr+0x4dc/0xeb4 fs/btrfs/inode.c:5344
       notify_change+0xb5c/0xe20 fs/attr.c:499
       do_truncate+0x188/0x20c fs/open.c:65
       vfs_truncate+0x23c/0x2b0 fs/open.c:111
       do_sys_truncate+0xec/0x1b4 fs/open.c:134
       __do_sys_truncate fs/open.c:146 [inline]
       __se_sys_truncate fs/open.c:144 [inline]
       __arm64_sys_truncate+0x5c/0x70 fs/open.c:144
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #0 (sb_internal#2){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain kernel/locking/lockdep.c:3825 [inline]
       __lock_acquire+0x27c8/0x6610 kernel/locking/lockdep.c:5049
       lock_acquire+0x20c/0x638 kernel/locking/lockdep.c:5662
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1891 [inline]
       sb_start_intwrite include/linux/fs.h:2013 [inline]
       start_transaction+0x5c0/0x1040 fs/btrfs/transaction.c:662
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781
       btrfs_dirty_inode+0xb0/0x1b8 fs/btrfs/inode.c:6287
       btrfs_update_time+0x170/0x18c fs/btrfs/inode.c:6329
       inode_update_time fs/inode.c:1958 [inline]
       touch_atime+0x368/0x7dc fs/inode.c:2031
       file_accessed include/linux/fs.h:2600 [inline]
       btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2053
       call_mmap include/linux/fs.h:2270 [inline]
       mmap_file+0x6c/0xc8 mm/util.c:1109
       __mmap_region mm/mmap.c:2772 [inline]
       mmap_region+0xc88/0x1860 mm/mmap.c:2916
       do_mmap+0xa64/0x1210 mm/mmap.c:1436
       vm_mmap_pgoff+0x194/0x298 mm/util.c:520
       ksys_mmap_pgoff+0x364/0x5a0 mm/mmap.c:1482
       __do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
       __se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
       __arm64_sys_mmap+0x108/0x120 arch/arm64/kernel/sys.c:21
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

other info that might help us debug this:

Chain exists of:
  sb_internal#2 --> &type->i_mutex_dir_key#2 --> &mm->mmap_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_lock);
                               lock(&type->i_mutex_dir_key#2);
                               lock(&mm->mmap_lock);
  lock(sb_internal#2);

 *** DEADLOCK ***

2 locks held by syz.4.506/8900:
 #0: ffff0000d5c57348 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff0000d5c57348 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x148/0x298 mm/util.c:518
 #1: ffff0000dd202460 (sb_writers#16){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2600 [inline]
 #1: ffff0000dd202460 (sb_writers#16){.+.+}-{0:0}, at: btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2053

stack backtrace:
CPU: 0 PID: 8900 Comm: syz.4.506 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/02/2026
Call trace:
 dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
 dump_stack+0x1c/0x5c lib/dump_stack.c:113
 print_circular_bug+0x148/0x1b0 kernel/locking/lockdep.c:2048
 check_noncircular+0x264/0x2f8 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3090 [inline]
 check_prevs_add kernel/locking/lockdep.c:3209 [inline]
 validate_chain kernel/locking/lockdep.c:3825 [inline]
 __lock_acquire+0x27c8/0x6610 kernel/locking/lockdep.c:5049
 lock_acquire+0x20c/0x638 kernel/locking/lockdep.c:5662
 percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
 __sb_start_write include/linux/fs.h:1891 [inline]
 sb_start_intwrite include/linux/fs.h:2013 [inline]
 start_transaction+0x5c0/0x1040 fs/btrfs/transaction.c:662
 btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781
 btrfs_dirty_inode+0xb0/0x1b8 fs/btrfs/inode.c:6287
 btrfs_update_time+0x170/0x18c fs/btrfs/inode.c:6329
 inode_update_time fs/inode.c:1958 [inline]
 touch_atime+0x368/0x7dc fs/inode.c:2031
 file_accessed include/linux/fs.h:2600 [inline]
 btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2053
 call_mmap include/linux/fs.h:2270 [inline]
 mmap_file+0x6c/0xc8 mm/util.c:1109
 __mmap_region mm/mmap.c:2772 [inline]
 mmap_region+0xc88/0x1860 mm/mmap.c:2916
 do_mmap+0xa64/0x1210 mm/mmap.c:1436
 vm_mmap_pgoff+0x194/0x298 mm/util.c:520
 ksys_mmap_pgoff+0x364/0x5a0 mm/mmap.c:1482
 __do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
 __se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
 __arm64_sys_mmap+0x108/0x120 arch/arm64/kernel/sys.c:21
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/04 08:00 linux-6.1.y fdb6fcb41cc7 fcece630 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 possible deadlock in btrfs_join_transaction
2026/06/14 18:43 linux-6.1.y 228da13e907e 1d2f3589 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 possible deadlock in btrfs_join_transaction
* Struck through repros no longer work on HEAD.