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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: 70d, last: 2d07h
▶ ▼ 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 Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 possible deadlock in btrfs_join_transaction 4 2 96d 117d 0/3 upstream: reported on 2025/05/06 20:52
upstream possible deadlock in btrfs_join_transaction btrfs 4 C 2 1006d 1011d 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 C error 62 10d 589d 0/3 upstream: reported C repro on 2024/01/20 21:24

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 Not tainted
------------------------------------------------------
syz.6.256/8116 is trying to acquire lock:
ffff0000c66da618 (sb_internal#4){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830

but task is already holding lock:
ffff0000dad181d0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:415 [inline]
ffff0000dad181d0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dc/0x45c mm/util.c:578

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:1560
       mmap_read_lock_killable+0x28/0x8c include/linux/mmap_lock.h:462
       get_mmap_lock_carefully mm/mmap_lock.c:286 [inline]
       lock_mm_and_find_vma+0x2a4/0x2d8 mm/mmap_lock.c:337
       do_page_fault+0x50c/0x13cc arch/arm64/mm/fault.c:674
       do_translation_fault+0xc4/0x114 arch/arm64/mm/fault.c:789
       do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:929
       el1_abort+0x3c/0x5c arch/arm64/kernel/entry-common.c:481
       el1h_64_sync_handler+0x50/0xfc arch/arm64/kernel/entry-common.c:597
       el1h_64_sync+0x6c/0x70 arch/arm64/kernel/entry.S:591
       __uaccess_mask_ptr arch/arm64/include/asm/uaccess.h:169 [inline]
       filldir64+0x2ec/0x6bc fs/readdir.c:379
       dir_emit include/linux/fs.h:3958 [inline]
       kernfs_fop_readdir+0x498/0x79c fs/kernfs/dir.c:1910
       iterate_dir+0x2dc/0x478 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+0x58/0x180 arch/arm64/kernel/entry-common.c:879
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x50/0xc0 kernel/locking/rwsem.c:1590
       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:2641
       btrfs_quota_enable+0x214/0x2208 fs/btrfs/qgroup.c:1022
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3667
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5318
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl fs/ioctl.c:584 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:584
       __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+0x58/0x180 arch/arm64/kernel/entry-common.c:879
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock_common+0x1d0/0x24ac kernel/locking/mutex.c:598
       __mutex_lock kernel/locking/mutex.c:760 [inline]
       mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
       btrfs_quota_enable+0x250/0x2208 fs/btrfs/qgroup.c:1051
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3667
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5318
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl fs/ioctl.c:584 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:584
       __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+0x58/0x180 arch/arm64/kernel/entry-common.c:879
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #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_start_transaction+0x34/0x44 fs/btrfs/transaction.c:816
       btrfs_rebuild_free_space_tree+0xac/0x75c fs/btrfs/free-space-tree.c:1339
       btrfs_start_pre_rw_mount+0xed8/0x1728 fs/btrfs/disk-io.c:3075
       open_ctree+0x2324/0x32c4 fs/btrfs/disk-io.c:3617
       btrfs_fill_super fs/btrfs/super.c:977 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1937 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2074 [inline]
       btrfs_get_tree+0xd5c/0x1590 fs/btrfs/super.c:2108
       vfs_get_tree+0x90/0x28c fs/super.c:1815
       do_new_mount+0x278/0x7f4 fs/namespace.c:3805
       path_mount+0x5b4/0xde0 fs/namespace.c:4120
       do_mount fs/namespace.c:4133 [inline]
       __do_sys_mount fs/namespace.c:4344 [inline]
       __se_sys_mount fs/namespace.c:4321 [inline]
       __arm64_sys_mount+0x3e8/0x468 fs/namespace.c:4321
       __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+0x58/0x180 arch/arm64/kernel/entry-common.c:879
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #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_start_transaction+0x34/0x44 fs/btrfs/transaction.c:816
       btrfs_rebuild_free_space_tree+0xac/0x75c fs/btrfs/free-space-tree.c:1339
       btrfs_start_pre_rw_mount+0xed8/0x1728 fs/btrfs/disk-io.c:3075
       open_ctree+0x2324/0x32c4 fs/btrfs/disk-io.c:3617
       btrfs_fill_super fs/btrfs/super.c:977 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1937 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2074 [inline]
       btrfs_get_tree+0xd5c/0x1590 fs/btrfs/super.c:2108
       vfs_get_tree+0x90/0x28c fs/super.c:1815
       do_new_mount+0x278/0x7f4 fs/namespace.c:3805
       path_mount+0x5b4/0xde0 fs/namespace.c:4120
       do_mount fs/namespace.c:4133 [inline]
       __do_sys_mount fs/namespace.c:4344 [inline]
       __se_sys_mount fs/namespace.c:4321 [inline]
       __arm64_sys_mount+0x3e8/0x468 fs/namespace.c:4321
       __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+0x58/0x180 arch/arm64/kernel/entry-common.c:879
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #0 (sb_internal#4){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237
       lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
       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:1798 [inline]
       sb_start_intwrite include/linux/fs.h:1981 [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:6216
       btrfs_update_time+0xa0/0xd0 fs/btrfs/inode.c:6250
       inode_update_time fs/inode.c:2075 [inline]
       touch_atime+0x2e4/0x818 fs/inode.c:2148
       file_accessed include/linux/fs.h:2663 [inline]
       btrfs_file_mmap_prepare+0xc4/0x130 fs/btrfs/file.c:2050
       vfs_mmap_prepare include/linux/fs.h:2294 [inline]
       call_mmap_prepare mm/vma.c:2585 [inline]
       __mmap_region mm/vma.c:2653 [inline]
       mmap_region+0x934/0x1d20 mm/vma.c:2739
       do_mmap+0x968/0xfac mm/mmap.c:558
       vm_mmap_pgoff+0x2d8/0x45c mm/util.c:580
       ksys_mmap_pgoff+0x394/0x5b8 mm/mmap.c:604
       __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+0x58/0x180 arch/arm64/kernel/entry-common.c:879
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

other info that might help us debug this:

Chain exists of:
  sb_internal#4 --> &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#4);

 *** DEADLOCK ***

2 locks held by syz.6.256/8116:
 #0: ffff0000dad181d0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:415 [inline]
 #0: ffff0000dad181d0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dc/0x45c mm/util.c:578
 #1: ffff0000c66da428 (sb_writers#19){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2663 [inline]
 #1: ffff0000c66da428 (sb_writers#19){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0xc4/0x130 fs/btrfs/file.c:2050

stack backtrace:
CPU: 1 UID: 0 PID: 8116 Comm: syz.6.256 Not tainted 6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (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:2043
 check_noncircular+0x154/0x174 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237
 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
 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:1798 [inline]
 sb_start_intwrite include/linux/fs.h:1981 [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:6216
 btrfs_update_time+0xa0/0xd0 fs/btrfs/inode.c:6250
 inode_update_time fs/inode.c:2075 [inline]
 touch_atime+0x2e4/0x818 fs/inode.c:2148
 file_accessed include/linux/fs.h:2663 [inline]
 btrfs_file_mmap_prepare+0xc4/0x130 fs/btrfs/file.c:2050
 vfs_mmap_prepare include/linux/fs.h:2294 [inline]
 call_mmap_prepare mm/vma.c:2585 [inline]
 __mmap_region mm/vma.c:2653 [inline]
 mmap_region+0x934/0x1d20 mm/vma.c:2739
 do_mmap+0x968/0xfac mm/mmap.c:558
 vm_mmap_pgoff+0x2d8/0x45c mm/util.c:580
 ksys_mmap_pgoff+0x394/0x5b8 mm/mmap.c:604
 __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+0x58/0x180 arch/arm64/kernel/entry-common.c:879
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/08/29 23:00 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 8f5ae30d69d7 3e1beec6 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 possible deadlock in btrfs_join_transaction
2025/08/25 08:12 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 8f5ae30d69d7 bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 possible deadlock in btrfs_join_transaction
2025/07/08 05:16 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 7482bb149b9f 4f67c4ae .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 possible deadlock in btrfs_join_transaction
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.