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possible deadlock in mnt_want_write (8)

Status: closed as dup on 2026/06/09 14:03
Subsystems: overlayfs
[Documentation on labels]
Reported-by: syzbot+1e5626d6fd59853cbfaa@syzkaller.appspotmail.com
First crash: 14d, last: 9h34m
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
5de1ead2-b73e-4f06-99fe-11ed865ad820 assessment-security 💥 possible deadlock in mnt_want_write (8) 2026/06/09 11:46 2026/06/09 11:46 2026/06/09 11:46 656e94c64cf6d2cf6e13f9bbe93a03e73688e3ba 
failed to run ["git" "-c" "core.hooksPath=/dev/null" "fetch" "--force" "--tags" "433dfd5a8a5d80bbf0669b14e9ed908911a52dd6" "ec7ef10b77a69d482f7c78c8236389e64a08eb98"]: exit status 128
fatal: remote er...
truncated to first 200 bytes; open job for full error
▶ ▼ Duplicate of
Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported
possible deadlock in lock_two_nondirectories (2) overlayfs ext4 prio:high 4 C error 12 1d08h 14d
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [overlayfs?] possible deadlock in mnt_want_write (8) 1 (2) 2026/06/09 14:03
▶ ▼ Similar bugs (12)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 possible deadlock in mnt_want_write missing-backport 4 C done 117 934d 1186d 0/3 auto-obsoleted due to no activity on 2024/10/15 12:27
upstream possible deadlock in mnt_want_write (6) kernfs 4 1 374d 370d 0/29 auto-obsoleted due to no activity on 2025/08/08 23:21
upstream possible deadlock in mnt_want_write fs 4 C done done 662 2080d 2888d 15/29 fixed on 2020/11/16 12:12
upstream possible deadlock in mnt_want_write (5) kernfs 4 1 525d 520d 0/29 auto-obsoleted due to no activity on 2025/04/20 18:48
linux-6.1 possible deadlock in mnt_want_write origin:upstream missing-backport 4 C done 56 935d 1179d 0/3 upstream: reported C repro on 2023/03/28 13:05
linux-4.19 possible deadlock in mnt_want_write romfs 4 C 730 1200d 2618d 0/1 upstream: reported C repro on 2019/04/19 16:54
android-49 possible deadlock in mnt_want_write 4 1 2870d 2870d 0/3 auto-closed as invalid on 2019/02/22 14:57
upstream possible deadlock in mnt_want_write (4) kernfs 4 1 650d 646d 0/29 auto-obsoleted due to no activity on 2024/12/16 14:12
upstream possible deadlock in mnt_want_write (2) integrity overlayfs 4 C done 867 961d 1830d 25/29 fixed on 2023/12/21 01:43
upstream possible deadlock in mnt_want_write (3) kernfs 4 9 797d 900d 0/29 auto-obsoleted due to no activity on 2024/07/22 10:45
upstream possible deadlock in mnt_want_write (7) fs 4 3 169d 172d 0/29 auto-obsoleted due to no activity on 2026/04/11 06:22
linux-4.14 possible deadlock in mnt_want_write ubifs 4 C 10467 1200d 2612d 0/1 upstream: reported C repro on 2019/04/25 05:09

Sample crash report:
loop4: detected capacity change from 0 to 1024
EXT4-fs (loop4): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.
evm: overlay not supported
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.4.218/5836 is trying to acquire lock:
ffff0000d2c9a410 (sb_writers#3){.+.+}-{0:0}, at: mnt_want_write+0x44/0x9c fs/namespace.c:493

but task is already holding lock:
ffff0000f2e0d368 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: inode_lock_killable include/linux/fs.h:1034 [inline]
ffff0000f2e0d368 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: do_truncate+0x174/0x22c fs/open.c:63

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}:
       down_write+0x50/0xc0 kernel/locking/rwsem.c:1625
       inode_lock include/linux/fs.h:1029 [inline]
       lock_two_nondirectories+0xc4/0x148 fs/inode.c:1254
       ext4_move_extents+0x194/0x3324 fs/ext4/move_extent.c:589
       __ext4_ioctl fs/ext4/ioctl.c:1657 [inline]
       ext4_ioctl+0x2a10/0x4280 fs/ext4/ioctl.c:1922
       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+0x98/0x244 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
       do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
       el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
       el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

-> #0 (sb_writers#3){.+.+}-{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+0x17c0/0x2ebc kernel/locking/lockdep.c:5237
       lock_acquire+0x140/0x364 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/super.h:19 [inline]
       sb_start_write+0x5c/0x294 include/linux/fs/super.h:125
       mnt_want_write+0x44/0x9c fs/namespace.c:493
       ovl_want_write+0x90/0xa0 fs/overlayfs/util.c:38
       ovl_setattr+0x238/0x4ac fs/overlayfs/inode.c:75
       notify_change+0x928/0xb7c fs/attr.c:556
       do_truncate+0x1a8/0x22c fs/open.c:68
       handle_truncate fs/namei.c:4307 [inline]
       do_open fs/namei.c:4703 [inline]
       path_openat+0x245c/0x2b88 fs/namei.c:4858
       do_file_open+0x1c8/0x2e8 fs/namei.c:4887
       do_sys_openat2+0x114/0x1e8 fs/open.c:1364
       do_sys_open+0xac/0xdc fs/open.c:1370
       __do_sys_openat fs/open.c:1386 [inline]
       __se_sys_openat fs/open.c:1381 [inline]
       __arm64_sys_openat+0xa0/0xbc fs/open.c:1381
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
       do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
       el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
       el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ovl_i_mutex_key[depth]);
                               lock(sb_writers#3);
                               lock(&ovl_i_mutex_key[depth]);
  rlock(sb_writers#3);

 *** DEADLOCK ***

2 locks held by syz.4.218/5836:
 #0: ffff0000cbc22410 (sb_writers#16){.+.+}-{0:0}, at: mnt_want_write+0x44/0x9c fs/namespace.c:493
 #1: ffff0000f2e0d368 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: inode_lock_killable include/linux/fs.h:1034 [inline]
 #1: ffff0000f2e0d368 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: do_truncate+0x174/0x22c fs/open.c:63

stack backtrace:
CPU: 1 UID: 0 PID: 5836 Comm: syz.4.218 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/02/2026
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+0x328/0x330 kernel/locking/lockdep.c:2043
 check_noncircular+0x158/0x174 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+0x17c0/0x2ebc kernel/locking/lockdep.c:5237
 lock_acquire+0x140/0x364 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/super.h:19 [inline]
 sb_start_write+0x5c/0x294 include/linux/fs/super.h:125
 mnt_want_write+0x44/0x9c fs/namespace.c:493
 ovl_want_write+0x90/0xa0 fs/overlayfs/util.c:38
 ovl_setattr+0x238/0x4ac fs/overlayfs/inode.c:75
 notify_change+0x928/0xb7c fs/attr.c:556
 do_truncate+0x1a8/0x22c fs/open.c:68
 handle_truncate fs/namei.c:4307 [inline]
 do_open fs/namei.c:4703 [inline]
 path_openat+0x245c/0x2b88 fs/namei.c:4858
 do_file_open+0x1c8/0x2e8 fs/namei.c:4887
 do_sys_openat2+0x114/0x1e8 fs/open.c:1364
 do_sys_open+0xac/0xdc fs/open.c:1370
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __arm64_sys_openat+0xa0/0xbc fs/open.c:1381
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
overlayfs: failed lookup in lower (/, name='file0', err=-40): overlapping layers

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/19 09:14 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci c2a9495bd873 d7ffd47b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 possible deadlock in mnt_want_write
2026/06/04 23:06 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci ec7ef10b77a6 197909be .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 possible deadlock in mnt_want_write
* Struck through repros no longer work on HEAD.