syzbot

 sign-in | mailing list | source | docs
🐞 Open [1571]
≡ Subsystems
🐞 Fixed [6330]
🐞 Invalid [16131]
⬇ Missing Backports [191]
≡ Crashes
Kernel Health Bugs/Month Bug Lifetimes Fuzzing
Total Repo Heatmap Subsystems Heatmap
💬 Send us feedback

possible deadlock in btrfs_join_transaction (2)

Status: upstream: reported on 2025/06/26 10:05
Subsystems: btrfs
[Documentation on labels]
Reported-by: syzbot+872fc61967352fcc3535@syzkaller.appspotmail.com
First crash: 5d00h, last: 5d00h
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [btrfs?] possible deadlock in btrfs_join_transaction (2) 0 (1) 2025/06/26 10:05
▶ ▼ Similar bugs (3)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 possible deadlock in btrfs_join_transaction 2 30d 51d 0/3 upstream: reported on 2025/05/06 20:52
upstream possible deadlock in btrfs_join_transaction btrfs C 2 940d 946d 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 C error 52 1d04h 523d 0/3 upstream: reported C repro on 2024/01/20 21:24

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc2-syzkaller-g9aa9b43d689e #0 Not tainted
------------------------------------------------------
syz.2.224/7634 is trying to acquire lock:
ffff0000c6b20618 (sb_internal#3){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830

but task is already holding lock:
ffff0000d0c2b7d0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:374 [inline]
ffff0000d0c2b7d0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x180/0x43c mm/util.c:577

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&mm->mmap_lock){++++}-{4:4}:
       down_read_killable+0x60/0x32c kernel/locking/rwsem.c:1547
       mmap_read_lock_killable+0x28/0x8c include/linux/mmap_lock.h:421
       get_mmap_lock_carefully mm/mmap_lock.c:197 [inline]
       lock_mm_and_find_vma+0x2a4/0x2d8 mm/mmap_lock.c:248
       do_page_fault+0x51c/0x1554 arch/arm64/mm/fault.c:668
       do_translation_fault+0xc4/0x114 arch/arm64/mm/fault.c:783
       do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:919
       el1_abort+0x3c/0x5c arch/arm64/kernel/entry-common.c:455
       el1h_64_sync_handler+0x50/0xcc arch/arm64/kernel/entry-common.c:533
       el1h_64_sync+0x6c/0x70 arch/arm64/kernel/entry.S:595
       __uaccess_mask_ptr arch/arm64/include/asm/uaccess.h:169 [inline]
       filldir64+0x2ec/0x6bc fs/readdir.c:379
       dir_emit include/linux/fs.h:3917 [inline]
       kernfs_fop_readdir+0x498/0x79c fs/kernfs/dir.c:1910
       iterate_dir+0x458/0x5e0 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:410 [inline]
       __se_sys_getdents64 fs/readdir.c:396 [inline]
       __arm64_sys_getdents64+0x110/0x2fc fs/readdir.c:396
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x58/0x17c arch/arm64/kernel/entry-common.c:767
       el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x50/0xc0 kernel/locking/rwsem.c:1577
       kernfs_add_one+0x48/0x60c fs/kernfs/dir.c:791
       kernfs_create_dir_ns+0xd4/0x12c fs/kernfs/dir.c:1093
       sysfs_create_dir_ns+0x114/0x24c fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x5a8/0xb20 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x118/0x17c lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x110/0x268 fs/btrfs/sysfs.c:2635
       btrfs_quota_enable+0x224/0x1c70 fs/btrfs/qgroup.c:1030
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3673
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5323
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl fs/ioctl.c:893 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:893
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x58/0x17c arch/arm64/kernel/entry-common.c:767
       el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock_common+0x1d0/0x2190 kernel/locking/mutex.c:602
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:799
       btrfs_quota_enable+0x270/0x1c70 fs/btrfs/qgroup.c:1059
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3673
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5323
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl fs/ioctl.c:893 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:893
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x58/0x17c arch/arm64/kernel/entry-common.c:767
       el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x190/0xb5c fs/btrfs/transaction.c:321
       start_transaction+0x778/0x155c fs/btrfs/transaction.c:705
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830
       __cow_file_range_inline+0x140/0xf14 fs/btrfs/inode.c:618
       cow_file_range_inline+0x27c/0x338 fs/btrfs/inode.c:690
       cow_file_range+0x324/0xc70 fs/btrfs/inode.c:1293
       btrfs_run_delalloc_range+0x33c/0xd7c fs/btrfs/inode.c:2348
       writepage_delalloc+0x8f0/0x103c fs/btrfs/extent_io.c:1386
       extent_writepage fs/btrfs/extent_io.c:1717 [inline]
       extent_write_cache_pages fs/btrfs/extent_io.c:2403 [inline]
       btrfs_writepages+0x115c/0x20dc fs/btrfs/extent_io.c:2536
       do_writepages+0x270/0x468 mm/page-writeback.c:2636
       __writeback_single_inode+0x15c/0x13e8 fs/fs-writeback.c:1680
       writeback_sb_inodes+0x558/0xe38 fs/fs-writeback.c:1976
       wb_writeback+0x3cc/0xd70 fs/fs-writeback.c:2156
       wb_do_writeback fs/fs-writeback.c:2303 [inline]
       wb_workfn+0x338/0xdc0 fs/fs-writeback.c:2343
       process_one_work+0x7e8/0x155c kernel/workqueue.c:3238
       process_scheduled_works kernel/workqueue.c:3321 [inline]
       worker_thread+0x958/0xed8 kernel/workqueue.c:3402
       kthread+0x5fc/0x75c kernel/kthread.c:464
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x164/0xb5c fs/btrfs/transaction.c:320
       start_transaction+0x778/0x155c fs/btrfs/transaction.c:705
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830
       __cow_file_range_inline+0x140/0xf14 fs/btrfs/inode.c:618
       cow_file_range_inline+0x27c/0x338 fs/btrfs/inode.c:690
       cow_file_range+0x324/0xc70 fs/btrfs/inode.c:1293
       btrfs_run_delalloc_range+0x33c/0xd7c fs/btrfs/inode.c:2348
       writepage_delalloc+0x8f0/0x103c fs/btrfs/extent_io.c:1386
       extent_writepage fs/btrfs/extent_io.c:1717 [inline]
       extent_write_cache_pages fs/btrfs/extent_io.c:2403 [inline]
       btrfs_writepages+0x115c/0x20dc fs/btrfs/extent_io.c:2536
       do_writepages+0x270/0x468 mm/page-writeback.c:2636
       __writeback_single_inode+0x15c/0x13e8 fs/fs-writeback.c:1680
       writeback_sb_inodes+0x558/0xe38 fs/fs-writeback.c:1976
       wb_writeback+0x3cc/0xd70 fs/fs-writeback.c:2156
       wb_do_writeback fs/fs-writeback.c:2303 [inline]
       wb_workfn+0x338/0xdc0 fs/fs-writeback.c:2343
       process_one_work+0x7e8/0x155c kernel/workqueue.c:3238
       process_scheduled_works kernel/workqueue.c:3321 [inline]
       worker_thread+0x958/0xed8 kernel/workqueue.c:3402
       kthread+0x5fc/0x75c kernel/kthread.c:464
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

-> #0 (sb_internal#3){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain kernel/locking/lockdep.c:3911 [inline]
       __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5240
       lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5871
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
       __sb_start_write include/linux/fs.h:1793 [inline]
       sb_start_intwrite include/linux/fs.h:1976 [inline]
       start_transaction+0x5bc/0x155c fs/btrfs/transaction.c:699
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830
       btrfs_dirty_inode+0x90/0x190 fs/btrfs/inode.c:6225
       btrfs_update_time+0xa0/0xd0 fs/btrfs/inode.c:6259
       inode_update_time fs/inode.c:2076 [inline]
       touch_atime+0x2e4/0x818 fs/inode.c:2149
       file_accessed include/linux/fs.h:2650 [inline]
       btrfs_file_mmap+0xac/0x118 fs/btrfs/file.c:1988
       call_mmap include/linux/fs.h:2284 [inline]
       mmap_file mm/internal.h:167 [inline]
       __mmap_new_file_vma mm/vma.c:2405 [inline]
       __mmap_new_vma mm/vma.c:2467 [inline]
       __mmap_region mm/vma.c:2622 [inline]
       mmap_region+0xe9c/0x1c0c mm/vma.c:2692
       do_mmap+0x968/0xfac mm/mmap.c:561
       vm_mmap_pgoff+0x2b8/0x43c mm/util.c:579
       ksys_mmap_pgoff+0x394/0x5b8 mm/mmap.c:607
       __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:35 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x58/0x17c arch/arm64/kernel/entry-common.c:767
       el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

other info that might help us debug this:

Chain exists of:
  sb_internal#3 --> &root->kernfs_rwsem --> &mm->mmap_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_lock);
                               lock(&root->kernfs_rwsem);
                               lock(&mm->mmap_lock);
  rlock(sb_internal#3);

 *** DEADLOCK ***

2 locks held by syz.2.224/7634:
 #0: ffff0000d0c2b7d0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:374 [inline]
 #0: ffff0000d0c2b7d0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x180/0x43c mm/util.c:577
 #1: ffff0000c6b20428 (sb_writers#23){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2650 [inline]
 #1: ffff0000c6b20428 (sb_writers#23){.+.+}-{0:0}, at: btrfs_file_mmap+0xac/0x118 fs/btrfs/file.c:1988

stack backtrace:
CPU: 1 UID: 0 PID: 7634 Comm: syz.2.224 Not tainted 6.16.0-rc2-syzkaller-g9aa9b43d689e #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:501 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 dump_stack+0x1c/0x28 lib/dump_stack.c:129
 print_circular_bug+0x324/0x32c kernel/locking/lockdep.c:2046
 check_noncircular+0x154/0x174 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain kernel/locking/lockdep.c:3911 [inline]
 __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5240
 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5871
 percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
 percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
 __sb_start_write include/linux/fs.h:1793 [inline]
 sb_start_intwrite include/linux/fs.h:1976 [inline]
 start_transaction+0x5bc/0x155c fs/btrfs/transaction.c:699
 btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830
 btrfs_dirty_inode+0x90/0x190 fs/btrfs/inode.c:6225
 btrfs_update_time+0xa0/0xd0 fs/btrfs/inode.c:6259
 inode_update_time fs/inode.c:2076 [inline]
 touch_atime+0x2e4/0x818 fs/inode.c:2149
 file_accessed include/linux/fs.h:2650 [inline]
 btrfs_file_mmap+0xac/0x118 fs/btrfs/file.c:1988
 call_mmap include/linux/fs.h:2284 [inline]
 mmap_file mm/internal.h:167 [inline]
 __mmap_new_file_vma mm/vma.c:2405 [inline]
 __mmap_new_vma mm/vma.c:2467 [inline]
 __mmap_region mm/vma.c:2622 [inline]
 mmap_region+0xe9c/0x1c0c mm/vma.c:2692
 do_mmap+0x968/0xfac mm/mmap.c:561
 vm_mmap_pgoff+0x2b8/0x43c mm/util.c:579
 ksys_mmap_pgoff+0x394/0x5b8 mm/mmap.c:607
 __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:35 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x58/0x17c arch/arm64/kernel/entry-common.c:767
 el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/22 09:54 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 9aa9b43d689e d6cdfb8a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 possible deadlock in btrfs_join_transaction
* Struck through repros no longer work on HEAD.