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possible deadlock in btrfs_join_transaction (2)

Status: upstream: reported on 2025/10/12 21:10
Reported-by: syzbot+c57b833e56d7e5d7faa0@syzkaller.appspotmail.com
First crash: 9d12h, last: 9d12h
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in btrfs_join_transaction (2) btrfs 4 6 10d 117d 0/29 upstream: reported on 2025/06/26 10:05
linux-6.1 possible deadlock in btrfs_join_transaction 4 2 147d 168d 0/3 auto-obsoleted due to no activity on 2025/09/04 19:00
upstream possible deadlock in btrfs_join_transaction btrfs 4 C 2 1057d 1063d 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 61d 640d 0/3 upstream: reported C repro on 2024/01/20 21:24

Sample crash report:
BTRFS info (device loop4): clearing compat-ro feature flag for FREE_SPACE_TREE (0x1)
BTRFS info (device loop4): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.856/7345 is trying to acquire lock:
ffff0000d2968650 (sb_internal#4){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:780

but task is already holding lock:
ffff0000c4143748 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
ffff0000c4143748 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x138/0x284 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:5852
       filldir64+0x2cc/0x8fc fs/readdir.c:335
       dir_emit_dot include/linux/fs.h:3701 [inline]
       dir_emit_dots include/linux/fs.h:3712 [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/0x318 fs/readdir.c:354
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 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+0x64/0x304 kernel/locking/rwsem.c:1520
       inode_lock_shared include/linux/fs.h:768 [inline]
       lookup_slow+0x4c/0x80 fs/namei.c:1706
       walk_component+0x270/0x364 fs/namei.c:1998
       lookup_last fs/namei.c:2455 [inline]
       path_lookupat+0x13c/0x3d0 fs/namei.c:2479
       filename_lookup+0x190/0x42c fs/namei.c:2508
       kern_path+0x48/0x6c fs/namei.c:2606
       is_same_device fs/btrfs/volumes.c:695 [inline]
       device_list_add+0x1208/0x1be0 fs/btrfs/volumes.c:928
       btrfs_scan_one_device+0x364/0x570 fs/btrfs/volumes.c:1461
       btrfs_mount_root+0x404/0x780 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:1039 [inline]
       vfs_kern_mount+0xdc/0x178 fs/namespace.c:1069
       btrfs_mount+0x2a0/0x8dc 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:3069
       path_mount+0x5b4/0xe78 fs/namespace.c:3399
       do_mount fs/namespace.c:3412 [inline]
       __do_sys_mount fs/namespace.c:3620 [inline]
       __se_sys_mount fs/namespace.c:3597 [inline]
       __arm64_sys_mount+0x49c/0x584 fs/namespace.c:3597
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 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+0x190/0x1f38 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+0xf0/0xd00 fs/btrfs/volumes.c:8064
       commit_cowonly_roots+0x16c/0x714 fs/btrfs/transaction.c:1297
       btrfs_commit_transaction+0x10bc/0x29f0 fs/btrfs/transaction.c:2427
       btrfs_sync_file+0xa4c/0xf44 fs/btrfs/file.c:2022
       vfs_fsync_range+0x168/0x188 fs/sync.c:188
       generic_write_sync include/linux/fs.h:2962 [inline]
       btrfs_do_write_iter+0xafc/0x1154 fs/btrfs/file.c:1691
       btrfs_file_write_iter+0x2c/0x3c fs/btrfs/file.c:1705
       call_write_iter include/linux/fs.h:2265 [inline]
       new_sync_write fs/read_write.c:491 [inline]
       vfs_write+0x5ac/0x7c4 fs/read_write.c:584
       ksys_write+0x120/0x210 fs/read_write.c:637
       __do_sys_write fs/read_write.c:649 [inline]
       __se_sys_write fs/read_write.c:646 [inline]
       __arm64_sys_write+0x7c/0x90 fs/read_write.c:646
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 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_info->reloc_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x190/0x1f38 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+0x434/0x104c fs/btrfs/transaction.c:730
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:766
       btrfs_create_common+0x13c/0x224 fs/btrfs/inode.c:6785
       btrfs_create+0x104/0x128 fs/btrfs/inode.c:6831
       lookup_open fs/namei.c:3482 [inline]
       open_last_lookups fs/namei.c:3550 [inline]
       path_openat+0x112c/0x2680 fs/namei.c:3780
       do_filp_open+0x174/0x344 fs/namei.c:3810
       do_sys_openat2+0x128/0x3d8 fs/open.c:1318
       do_sys_open fs/open.c:1334 [inline]
       __do_sys_openat fs/open.c:1350 [inline]
       __se_sys_openat fs/open.c:1345 [inline]
       __arm64_sys_openat+0x120/0x154 fs/open.c:1345
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 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+0x180/0xb6c fs/btrfs/transaction.c:303
       start_transaction+0x854/0x104c fs/btrfs/transaction.c:667
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:766
       btrfs_create_common+0x13c/0x224 fs/btrfs/inode.c:6785
       btrfs_create+0x104/0x128 fs/btrfs/inode.c:6831
       lookup_open fs/namei.c:3482 [inline]
       open_last_lookups fs/namei.c:3550 [inline]
       path_openat+0x112c/0x2680 fs/namei.c:3780
       do_filp_open+0x174/0x344 fs/namei.c:3810
       do_sys_openat2+0x128/0x3d8 fs/open.c:1318
       do_sys_open fs/open.c:1334 [inline]
       __do_sys_openat fs/open.c:1350 [inline]
       __se_sys_openat fs/open.c:1345 [inline]
       __arm64_sys_openat+0x120/0x154 fs/open.c:1345
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 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+0x154/0xb6c fs/btrfs/transaction.c:302
       start_transaction+0x854/0x104c fs/btrfs/transaction.c:667
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:766
       btrfs_create_common+0x13c/0x224 fs/btrfs/inode.c:6785
       btrfs_create+0x104/0x128 fs/btrfs/inode.c:6831
       lookup_open fs/namei.c:3482 [inline]
       open_last_lookups fs/namei.c:3550 [inline]
       path_openat+0x112c/0x2680 fs/namei.c:3780
       do_filp_open+0x174/0x344 fs/namei.c:3810
       do_sys_openat2+0x128/0x3d8 fs/open.c:1318
       do_sys_open fs/open.c:1334 [inline]
       __do_sys_openat fs/open.c:1350 [inline]
       __se_sys_openat fs/open.c:1345 [inline]
       __arm64_sys_openat+0x120/0x154 fs/open.c:1345
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 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#4){.+.+}-{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+0x293c/0x6544 kernel/locking/lockdep.c:5049
       lock_acquire+0x20c/0x644 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+0x5c4/0x104c fs/btrfs/transaction.c:661
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:780
       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+0x364/0x7d0 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+0xccc/0x18d8 mm/mmap.c:2916
       do_mmap+0x9dc/0x11f4 mm/mmap.c:1436
       vm_mmap_pgoff+0x184/0x284 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+0x98/0x2bc arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x138 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#4 --> &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#4);

 *** DEADLOCK ***

2 locks held by syz.4.856/7345:
 #0: ffff0000c4143748 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff0000c4143748 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0x138/0x284 mm/util.c:518
 #1: ffff0000d2968460 (sb_writers#17){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2600 [inline]
 #1: ffff0000d2968460 (sb_writers#17){.+.+}-{0:0}, at: btrfs_file_mmap+0xb0/0x11c fs/btrfs/file.c:2053

stack backtrace:
CPU: 1 PID: 7345 Comm: syz.4.856 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
Call trace:
 dump_backtrace+0x1c8/0x1f4 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+0xf8/0x160 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+0x240/0x2d4 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+0x293c/0x6544 kernel/locking/lockdep.c:5049
 lock_acquire+0x20c/0x644 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+0x5c4/0x104c fs/btrfs/transaction.c:661
 btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:780
 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+0x364/0x7d0 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+0xccc/0x18d8 mm/mmap.c:2916
 do_mmap+0x9dc/0x11f4 mm/mmap.c:1436
 vm_mmap_pgoff+0x184/0x284 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+0x98/0x2bc arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x138 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 (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/12 21:10 linux-6.1.y 882efbdd9d34 ff1712fe .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.