possible deadlock in btrfs_join_transaction (3)

Status: auto-obsoleted due to no activity on 2026/05/20 06:23
Reported-by: syzbot+8d6efc2849cc988f03e6@syzkaller.appspotmail.com
First crash: 208d, last: 188d
▶ ▼ 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 227d 416d 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 446d 467d 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 308d 308d 0/3 auto-obsoleted due to no activity on 2026/01/20 21:10
linux-6.1 possible deadlock in btrfs_join_transaction (4) 4 2 43d 63d 0/3 upstream: reported on 2026/06/14 18:43
upstream possible deadlock in btrfs_join_transaction btrfs 4 syz, C 2 1356d 1361d 0/29 auto-obsoleted due to no activity on 2023/03/29 11:54
linux-5.15 possible deadlock in btrfs_join_transaction origin:upstream 4 syz, C error 62 68d 939d 0/3 upstream: reported C repro on 2024/01/20 21:24

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.467/6897 is trying to acquire lock:
ffff0000dd996650 (sb_internal#3){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781

but task is already holding lock:
ffff0000cc4e9348 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
ffff0000cc4e9348 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x144/0x294 mm/util.c:518

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&mm->mmap_lock){++++}-{3:3}:
       __might_fault+0xc4/0x124 mm/memory.c:5850
       filldir64+0x2cc/0x8fc fs/readdir.c:335
       dir_emit_dot include/linux/fs.h:3698 [inline]
       dir_emit_dots include/linux/fs.h:3709 [inline]
       dcache_readdir+0x140/0x62c fs/libfs.c:197
       iterate_dir+0x1f0/0x4cc fs/readdir.c:-1
       __do_sys_getdents64 fs/readdir.c:369 [inline]
       __se_sys_getdents64 fs/readdir.c:354 [inline]
       __arm64_sys_getdents64+0x11c/0x320 fs/readdir.c:354
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x130 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 (&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+0x4c/0x80 fs/namei.c:1714
       walk_component+0x270/0x364 fs/namei.c:2006
       lookup_last fs/namei.c:2463 [inline]
       path_lookupat+0x13c/0x3d0 fs/namei.c:2487
       filename_lookup+0x1c4/0x480 fs/namei.c:2516
       kern_path+0x48/0x6c fs/namei.c:2614
       is_same_device fs/btrfs/volumes.c:695 [inline]
       device_list_add+0x129c/0x1c84 fs/btrfs/volumes.c:928
       btrfs_scan_one_device+0x368/0x57c fs/btrfs/volumes.c:1461
       btrfs_mount_root+0x45c/0x7d0 fs/btrfs/super.c:1796
       legacy_get_tree+0xd4/0x16c fs/fs_context.c:632
       vfs_get_tree+0x90/0x274 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+0xd4/0x16c fs/fs_context.c:632
       vfs_get_tree+0x90/0x274 fs/super.c:1573
       do_new_mount+0x228/0x810 fs/namespace.c:3078
       path_mount+0x5bc/0xe80 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+0x49c/0x59c fs/namespace.c:3606
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x130 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

-> #3 (&fs_devs->device_list_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x190/0x1f60 kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       insert_dev_extents fs/btrfs/block-group.c:2520 [inline]
       btrfs_create_pending_block_groups+0x470/0xda0 fs/btrfs/block-group.c:2571
       __btrfs_end_transaction+0x134/0x5f0 fs/btrfs/transaction.c:1013
       btrfs_end_transaction+0x24/0x34 fs/btrfs/transaction.c:1052
       flush_space+0x838/0xc94 fs/btrfs/space-info.c:818
       btrfs_async_reclaim_metadata_space+0x25c/0x30c fs/btrfs/space-info.c:1128
       process_one_work+0x7f8/0x13a4 kernel/workqueue.c:2292
       worker_thread+0x8c4/0xfec kernel/workqueue.c:2439
       kthread+0x250/0x2d8 kernel/kthread.c:376
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:850

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x180/0xb68 fs/btrfs/transaction.c:303
       start_transaction+0x858/0x1050 fs/btrfs/transaction.c:668
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781
       btrfs_commit_super+0x8c/0xc8 fs/btrfs/disk-io.c:4538
       close_ctree+0x400/0xa94 fs/btrfs/disk-io.c:4748
       btrfs_put_super+0x70/0x80 fs/btrfs/super.c:397
       generic_shutdown_super+0x130/0x324 fs/super.c:501
       kill_anon_super+0x4c/0x80 fs/super.c:1128
       btrfs_kill_super+0x40/0x58 fs/btrfs/super.c:2448
       deactivate_locked_super+0xac/0x120 fs/super.c:332
       deactivate_super+0xe4/0x104 fs/super.c:363
       cleanup_mnt+0x390/0x418 fs/namespace.c:1191
       __cleanup_mnt+0x20/0x30 fs/namespace.c:1198
       task_work_run+0x1ec/0x278 kernel/task_work.c:203
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       do_notify_resume+0x1fa0/0x2aa4 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

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x154/0xb68 fs/btrfs/transaction.c:302
       start_transaction+0x858/0x1050 fs/btrfs/transaction.c:668
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781
       btrfs_commit_super+0x8c/0xc8 fs/btrfs/disk-io.c:4538
       close_ctree+0x400/0xa94 fs/btrfs/disk-io.c:4748
       btrfs_put_super+0x70/0x80 fs/btrfs/super.c:397
       generic_shutdown_super+0x130/0x324 fs/super.c:501
       kill_anon_super+0x4c/0x80 fs/super.c:1128
       btrfs_kill_super+0x40/0x58 fs/btrfs/super.c:2448
       deactivate_locked_super+0xac/0x120 fs/super.c:332
       deactivate_super+0xe4/0x104 fs/super.c:363
       cleanup_mnt+0x390/0x418 fs/namespace.c:1191
       __cleanup_mnt+0x20/0x30 fs/namespace.c:1198
       task_work_run+0x1ec/0x278 kernel/task_work.c:203
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       do_notify_resume+0x1fa0/0x2aa4 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

-> #0 (sb_internal#3){.+.+}-{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+0x2880/0x6800 kernel/locking/lockdep.c:5049
       lock_acquire+0x20c/0x63c 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+0x5c4/0x1050 fs/btrfs/transaction.c:662
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781
       btrfs_dirty_inode+0xb4/0x1c0 fs/btrfs/inode.c:6277
       btrfs_update_time+0x170/0x18c fs/btrfs/inode.c:6319
       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+0xcec/0x1900 mm/mmap.c:2916
       do_mmap+0x9cc/0x1138 mm/mmap.c:1436
       vm_mmap_pgoff+0x190/0x294 mm/util.c:520
       ksys_mmap_pgoff+0x3b8/0x5a0 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+0xf8/0x110 arch/arm64/kernel/sys.c:21
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x130 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#3 --> &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#3);

 *** DEADLOCK ***

2 locks held by syz.1.467/6897:
 #0: ffff0000cc4e9348 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff0000cc4e9348 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x144/0x294 mm/util.c:518
 #1: ffff0000dd996460 (sb_writers#14){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2600 [inline]
 #1: ffff0000dd996460 (sb_writers#14){.+.+}-{0:0}, at: btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2053

stack backtrace:
CPU: 0 PID: 6897 Comm: syz.1.467 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
Call trace:
 dump_backtrace+0x1c0/0x1ec 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+0x2880/0x6800 kernel/locking/lockdep.c:5049
 lock_acquire+0x20c/0x63c 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+0x5c4/0x1050 fs/btrfs/transaction.c:662
 btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781
 btrfs_dirty_inode+0xb4/0x1c0 fs/btrfs/inode.c:6277
 btrfs_update_time+0x170/0x18c fs/btrfs/inode.c:6319
 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+0xcec/0x1900 mm/mmap.c:2916
 do_mmap+0x9cc/0x1138 mm/mmap.c:1436
 vm_mmap_pgoff+0x190/0x294 mm/util.c:520
 ksys_mmap_pgoff+0x3b8/0x5a0 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+0xf8/0x110 arch/arm64/kernel/sys.c:21
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x130 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
2026/02/09 06:23 linux-6.1.y 0182cb5b74ee 4c131dc4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 possible deadlock in btrfs_join_transaction
2026/01/20 21:40 linux-6.1.y cd9b81672742 06648d9c .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.