possible deadlock in btrfs_page_mkwrite

Status: auto-obsoleted due to no activity on 2026/03/09 08:20
Subsystems: btrfs
[Documentation on labels]
Reported-by: syzbot+8ff80a43de91ba2d80fc@syzkaller.appspotmail.com
First crash: 261d, last: 261d
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [btrfs?] possible deadlock in btrfs_page_mkwrite 0 (1) 2025/12/03 08:21
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 possible deadlock in btrfs_page_mkwrite 4 2 759d 847d 0/3 auto-obsoleted due to no activity on 2024/10/27 17:02
linux-5.15 possible deadlock in btrfs_page_mkwrite (2) 4 1 631d 631d 0/3 auto-obsoleted due to no activity on 2025/03/04 04:23

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.810/10993 is trying to acquire lock:
ffff0000f98b59b8 (&ei->i_mmap_lock){++++}-{4:4}, at: btrfs_page_mkwrite+0x5a4/0x1714 fs/btrfs/file.c:1919

but task is already holding lock:
ffff0000cadb8518 (sb_pagefaults#7){.+.+}-{0:0}, at: do_page_mkwrite+0x138/0x2b8 mm/memory.c:3489

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (sb_pagefaults#7){.+.+}-{0:0}:
       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:1916 [inline]
       sb_start_pagefault include/linux/fs.h:2081 [inline]
       btrfs_page_mkwrite+0x284/0x1714 fs/btrfs/file.c:1874
       do_page_mkwrite+0x138/0x2b8 mm/memory.c:3489
       do_shared_fault mm/memory.c:5792 [inline]
       do_fault mm/memory.c:5854 [inline]
       do_pte_missing mm/memory.c:4362 [inline]
       handle_pte_fault mm/memory.c:6234 [inline]
       __handle_mm_fault+0x178c/0x4798 mm/memory.c:6366
       handle_mm_fault+0x274/0x7fc mm/memory.c:6535
       do_page_fault+0x57c/0x13cc arch/arm64/mm/fault.c:700
       do_translation_fault+0xc4/0x114 arch/arm64/mm/fault.c:793
       do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:933
       el0_da+0x64/0x230 arch/arm64/kernel/entry-common.c:540
       el0t_64_sync_handler+0x90/0x12c arch/arm64/kernel/entry-common.c:746
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #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:377
       get_mmap_lock_carefully mm/mmap_lock.c:377 [inline]
       lock_mm_and_find_vma+0x2a4/0x2d8 mm/mmap_lock.c:428
       do_page_fault+0x50c/0x13cc arch/arm64/mm/fault.c:678
       do_translation_fault+0xc4/0x114 arch/arm64/mm/fault.c:793
       do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:933
       el1_abort+0x40/0x64 arch/arm64/kernel/entry-common.c:303
       el1h_64_sync_handler+0x50/0xfc arch/arm64/kernel/entry-common.c:437
       el1h_64_sync+0x6c/0x70 arch/arm64/kernel/entry.S:591
       __uaccess_mask_ptr arch/arm64/include/asm/uaccess.h:169 [inline]
       filldir64+0x314/0x6bc fs/readdir.c:381
       dir_emit include/linux/fs.h:3988 [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+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       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:2645
       btrfs_quota_enable+0x210/0x2438 fs/btrfs/qgroup.c:1022
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3667
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5333
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock_common+0x1d0/0x2678 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+0x24c/0x2438 fs/btrfs/qgroup.c:1051
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3667
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5333
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       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/0x6c0 fs/btrfs/free-space-tree.c:1340
       btrfs_start_pre_rw_mount+0xed8/0x1728 fs/btrfs/disk-io.c:3062
       open_ctree+0x24cc/0x358c fs/btrfs/disk-io.c:3619
       btrfs_fill_super fs/btrfs/super.c:987 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1951 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2094 [inline]
       btrfs_get_tree+0xd94/0x15dc fs/btrfs/super.c:2128
       vfs_get_tree+0x90/0x28c fs/super.c:1758
       fc_mount fs/namespace.c:1199 [inline]
       do_new_mount_fc fs/namespace.c:3642 [inline]
       do_new_mount+0x284/0x944 fs/namespace.c:3718
       path_mount+0x5b4/0xdfc fs/namespace.c:4028
       do_mount fs/namespace.c:4041 [inline]
       __do_sys_mount fs/namespace.c:4229 [inline]
       __se_sys_mount fs/namespace.c:4206 [inline]
       __arm64_sys_mount+0x3e8/0x468 fs/namespace.c:4206
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       __lock_release kernel/locking/lockdep.c:5574 [inline]
       lock_release+0x198/0x39c kernel/locking/lockdep.c:5889
       percpu_up_read include/linux/percpu-rwsem.h:112 [inline]
       __sb_end_write include/linux/fs.h:1911 [inline]
       sb_end_intwrite+0x3c/0x348 include/linux/fs.h:2028
       __btrfs_end_transaction+0x1f4/0x5f4 fs/btrfs/transaction.c:1076
       btrfs_end_transaction+0x24/0x34 fs/btrfs/transaction.c:1110
       __btrfs_prealloc_file_range+0x77c/0xb28 fs/btrfs/inode.c:9145
       btrfs_prealloc_file_range+0x60/0x7c fs/btrfs/inode.c:9159
       btrfs_zero_range+0x928/0xb7c fs/btrfs/file.c:3070
       btrfs_fallocate+0x8ec/0x1734 fs/btrfs/file.c:3181
       vfs_fallocate+0x52c/0x668 fs/open.c:342
       ksys_fallocate fs/open.c:366 [inline]
       __do_sys_fallocate fs/open.c:371 [inline]
       __se_sys_fallocate fs/open.c:369 [inline]
       __arm64_sys_fallocate+0xbc/0x10c fs/open.c:369
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #0 (&ei->i_mmap_lock){++++}-{4:4}:
       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
       down_read+0x58/0x2f8 kernel/locking/rwsem.c:1537
       btrfs_page_mkwrite+0x5a4/0x1714 fs/btrfs/file.c:1919
       do_page_mkwrite+0x138/0x2b8 mm/memory.c:3489
       do_shared_fault mm/memory.c:5792 [inline]
       do_fault mm/memory.c:5854 [inline]
       do_pte_missing mm/memory.c:4362 [inline]
       handle_pte_fault mm/memory.c:6234 [inline]
       __handle_mm_fault+0x178c/0x4798 mm/memory.c:6366
       handle_mm_fault+0x274/0x7fc mm/memory.c:6535
       do_page_fault+0x57c/0x13cc arch/arm64/mm/fault.c:700
       do_translation_fault+0xc4/0x114 arch/arm64/mm/fault.c:793
       do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:933
       el0_da+0x64/0x230 arch/arm64/kernel/entry-common.c:540
       el0t_64_sync_handler+0x90/0x12c arch/arm64/kernel/entry-common.c:746
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

other info that might help us debug this:

Chain exists of:
  &ei->i_mmap_lock --> &mm->mmap_lock --> sb_pagefaults#7

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(sb_pagefaults#7);
                               lock(&mm->mmap_lock);
                               lock(sb_pagefaults#7);
  rlock(&ei->i_mmap_lock);

 *** DEADLOCK ***

2 locks held by syz.1.810/10993:
 #0: ffff0000cf866790 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:387 [inline]
 #0: ffff0000cf866790 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:368 [inline]
 #0: ffff0000cf866790 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x38/0x2d8 mm/mmap_lock.c:428
 #1: ffff0000cadb8518 (sb_pagefaults#7){.+.+}-{0:0}, at: do_page_mkwrite+0x138/0x2b8 mm/memory.c:3489

stack backtrace:
CPU: 0 UID: 0 PID: 10993 Comm: syz.1.810 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
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
 down_read+0x58/0x2f8 kernel/locking/rwsem.c:1537
 btrfs_page_mkwrite+0x5a4/0x1714 fs/btrfs/file.c:1919
 do_page_mkwrite+0x138/0x2b8 mm/memory.c:3489
 do_shared_fault mm/memory.c:5792 [inline]
 do_fault mm/memory.c:5854 [inline]
 do_pte_missing mm/memory.c:4362 [inline]
 handle_pte_fault mm/memory.c:6234 [inline]
 __handle_mm_fault+0x178c/0x4798 mm/memory.c:6366
 handle_mm_fault+0x274/0x7fc mm/memory.c:6535
 do_page_fault+0x57c/0x13cc arch/arm64/mm/fault.c:700
 do_translation_fault+0xc4/0x114 arch/arm64/mm/fault.c:793
 do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:933
 el0_da+0x64/0x230 arch/arm64/kernel/entry-common.c:540
 el0t_64_sync_handler+0x90/0x12c arch/arm64/kernel/entry-common.c:746
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/29 08:19 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 05c93f3395ed d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 possible deadlock in btrfs_page_mkwrite
* Struck through repros no longer work on HEAD.