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possible deadlock in btrfs_join_transaction (4)

Status: upstream: reported on 2026/06/14 18:43
Reported-by: syzbot+8d1fbb49d58ce1fcca78@syzkaller.appspotmail.com
First crash: 10d, last: 10d
▶ ▼ 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 175d 364d 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 393d 414d 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 255d 255d 0/3 auto-obsoleted due to no activity on 2026/01/20 21:10
upstream possible deadlock in btrfs_join_transaction btrfs 4 C 2 1303d 1309d 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 136d 155d 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 C error 62 16d 886d 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.8.1037/8437 is trying to acquire lock:
ffff0000eaa48650 (sb_internal#3){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:781

but task is already holding lock:
ffff0000eaa48558 (sb_pagefaults#4){.+.+}-{0:0}, at: do_page_mkwrite+0x13c/0x358 mm/memory.c:3009

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (sb_pagefaults#4){.+.+}-{0:0}:
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1891 [inline]
       sb_start_pagefault include/linux/fs.h:1995 [inline]
       btrfs_page_mkwrite+0x198/0xb88 fs/btrfs/inode.c:8613
       do_page_mkwrite+0x13c/0x358 mm/memory.c:3009
       wp_page_shared+0x148/0x540 mm/memory.c:3358
       do_wp_page+0xca0/0xeec mm/memory.c:3508
       handle_pte_fault mm/memory.c:5047 [inline]
       __handle_mm_fault mm/memory.c:5171 [inline]
       handle_mm_fault+0x1514/0x2fb0 mm/memory.c:5292
       __do_page_fault arch/arm64/mm/fault.c:499 [inline]
       do_page_fault+0x310/0x98c arch/arm64/mm/fault.c:583
       do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:804
       el0_da+0x70/0x144 arch/arm64/kernel/entry-common.c:515
       el0t_64_sync_handler+0x90/0xf0 arch/arm64/kernel/entry-common.c:658
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #6 (&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+0x98/0x290 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

-> #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+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+0x98/0x290 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 (&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
       btrfs_run_dev_stats+0xf8/0xdc8 fs/btrfs/volumes.c:8071
       commit_cowonly_roots+0x170/0x71c fs/btrfs/transaction.c:1298
       btrfs_commit_transaction+0x10e8/0x2884 fs/btrfs/transaction.c:2444
       btrfs_rebuild_free_space_tree+0x2e8/0x6d8 fs/btrfs/free-space-tree.c:1347
       btrfs_start_pre_rw_mount+0x2c8/0x658 fs/btrfs/disk-io.c:3215
       open_ctree+0x1e44/0x2604 fs/btrfs/disk-io.c:3812
       btrfs_fill_super+0x1b4/0x2d4 fs/btrfs/super.c:1469
       btrfs_mount_root+0x780/0x7d0 fs/btrfs/super.c:1834
       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+0x98/0x290 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_info->reloc_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
       btrfs_record_root_in_trans fs/btrfs/transaction.c:488 [inline]
       start_transaction+0x434/0x1050 fs/btrfs/transaction.c:731
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:767
       btrfs_create_common+0x148/0x240 fs/btrfs/inode.c:6812
       btrfs_create+0x104/0x128 fs/btrfs/inode.c:6858
       lookup_open fs/namei.c:3490 [inline]
       open_last_lookups fs/namei.c:3558 [inline]
       path_openat+0xe18/0x26bc fs/namei.c:3788
       do_filp_open+0x194/0x384 fs/namei.c:3818
       do_sys_openat2+0x134/0x3f4 fs/open.c:1320
       do_sys_open fs/open.c:1336 [inline]
       __do_sys_openat fs/open.c:1352 [inline]
       __se_sys_openat fs/open.c:1347 [inline]
       __arm64_sys_openat+0x118/0x14c fs/open.c:1347
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x290 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

-> #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_start_transaction+0x34/0x44 fs/btrfs/transaction.c:767
       btrfs_rebuild_free_space_tree+0xbc/0x6d8 fs/btrfs/free-space-tree.c:1320
       btrfs_start_pre_rw_mount+0x2c8/0x658 fs/btrfs/disk-io.c:3215
       open_ctree+0x1e44/0x2604 fs/btrfs/disk-io.c:3812
       btrfs_fill_super+0x1b4/0x2d4 fs/btrfs/super.c:1469
       btrfs_mount_root+0x780/0x7d0 fs/btrfs/super.c:1834
       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+0x98/0x290 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

-> #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_start_transaction+0x34/0x44 fs/btrfs/transaction.c:767
       btrfs_rebuild_free_space_tree+0xbc/0x6d8 fs/btrfs/free-space-tree.c:1320
       btrfs_start_pre_rw_mount+0x2c8/0x658 fs/btrfs/disk-io.c:3215
       open_ctree+0x1e44/0x2604 fs/btrfs/disk-io.c:3812
       btrfs_fill_super+0x1b4/0x2d4 fs/btrfs/super.c:1469
       btrfs_mount_root+0x780/0x7d0 fs/btrfs/super.c:1834
       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+0x98/0x290 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

-> #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:6285
       btrfs_update_time+0x170/0x18c fs/btrfs/inode.c:6327
       inode_update_time fs/inode.c:1958 [inline]
       __file_update_time+0xc0/0x21c fs/inode.c:2147
       file_update_time+0x270/0x2ec fs/inode.c:2178
       btrfs_page_mkwrite+0x39c/0xb88 fs/btrfs/inode.c:8629
       do_page_mkwrite+0x13c/0x358 mm/memory.c:3009
       wp_page_shared+0x148/0x540 mm/memory.c:3358
       do_wp_page+0xca0/0xeec mm/memory.c:3508
       handle_pte_fault mm/memory.c:5047 [inline]
       __handle_mm_fault mm/memory.c:5171 [inline]
       handle_mm_fault+0x1514/0x2fb0 mm/memory.c:5292
       __do_page_fault arch/arm64/mm/fault.c:499 [inline]
       do_page_fault+0x310/0x98c arch/arm64/mm/fault.c:583
       do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:804
       el0_da+0x70/0x144 arch/arm64/kernel/entry-common.c:515
       el0t_64_sync_handler+0x90/0xf0 arch/arm64/kernel/entry-common.c:658
       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 --> &mm->mmap_lock --> sb_pagefaults#4

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sb_pagefaults#4);
                               lock(&mm->mmap_lock);
                               lock(sb_pagefaults#4);
  lock(sb_internal#3);

 *** DEADLOCK ***

2 locks held by syz.8.1037/8437:
 #0: ffff0000cd2d3d48 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_trylock include/linux/mmap_lock.h:136 [inline]
 #0: ffff0000cd2d3d48 (&mm->mmap_lock){++++}-{3:3}, at: get_mmap_lock_carefully mm/memory.c:5320 [inline]
 #0: ffff0000cd2d3d48 (&mm->mmap_lock){++++}-{3:3}, at: lock_mm_and_find_vma+0x38/0x2e0 mm/memory.c:5382
 #1: ffff0000eaa48558 (sb_pagefaults#4){.+.+}-{0:0}, at: do_page_mkwrite+0x13c/0x358 mm/memory.c:3009

stack backtrace:
CPU: 0 PID: 8437 Comm: syz.8.1037 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/02/2026
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:6285
 btrfs_update_time+0x170/0x18c fs/btrfs/inode.c:6327
 inode_update_time fs/inode.c:1958 [inline]
 __file_update_time+0xc0/0x21c fs/inode.c:2147
 file_update_time+0x270/0x2ec fs/inode.c:2178
 btrfs_page_mkwrite+0x39c/0xb88 fs/btrfs/inode.c:8629
 do_page_mkwrite+0x13c/0x358 mm/memory.c:3009
 wp_page_shared+0x148/0x540 mm/memory.c:3358
 do_wp_page+0xca0/0xeec mm/memory.c:3508
 handle_pte_fault mm/memory.c:5047 [inline]
 __handle_mm_fault mm/memory.c:5171 [inline]
 handle_mm_fault+0x1514/0x2fb0 mm/memory.c:5292
 __do_page_fault arch/arm64/mm/fault.c:499 [inline]
 do_page_fault+0x310/0x98c arch/arm64/mm/fault.c:583
 do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:804
 el0_da+0x70/0x144 arch/arm64/kernel/entry-common.c:515
 el0t_64_sync_handler+0x90/0xf0 arch/arm64/kernel/entry-common.c:658
 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
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.