[v6.6] possible deadlock in kernfs_fop_write_iter
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syzbot
Aug 27, 2025, 5:08:31 PM8/27/25
to syzkaller...@googlegroups.com
Hello,
syzbot found the following issue on:
HEAD commit: bb9c90ab9c5a Linux 6.6.102
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1486cfbc580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7b989b97a0687b0a
dashboard link: https://syzkaller.appspot.com/bug?extid=91b0074eab4a94ac90ae
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/44e2224124c3/disk-bb9c90ab.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/33e0aef7ff42/vmlinux-bb9c90ab.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0515bc436228/bzImage-bb9c90ab.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+91b007...@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
6.6.102-syzkaller #0 Not tainted
------------------------------------------------------
syz.2.15109/16283 is trying to acquire lock:
ffff88805e870088 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e9/0x4d0 fs/kernfs/file.c:325
but task is already holding lock:
ffff888051ae1068 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x1a0/0xc50 fs/splice.c:683
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&pipe->mutex/1){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x129/0xcc0 kernel/locking/mutex.c:747
__pipe_lock fs/pipe.c:103 [inline]
pipe_write+0x1c7/0x1af0 fs/pipe.c:444
__kernel_write_iter+0x274/0x670 fs/read_write.c:517
__kernel_write+0xf0/0x140 fs/read_write.c:537
autofs_write fs/autofs/waitq.c:57 [inline]
autofs_notify_daemon+0x6ff/0xdc0 fs/autofs/waitq.c:164
autofs_wait+0x1021/0x1a40 fs/autofs/waitq.c:426
autofs_mount_wait+0x16b/0x320 fs/autofs/root.c:255
autofs_d_automount+0x392/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1370 [inline]
__traverse_mounts+0x2fa/0x5a0 fs/namei.c:1415
traverse_mounts fs/namei.c:1444 [inline]
handle_mounts fs/namei.c:1547 [inline]
step_into+0x526/0xf10 fs/namei.c:1840
open_last_lookups fs/namei.c:3579 [inline]
path_openat+0x16bb/0x3190 fs/namei.c:3786
do_filp_open+0x1c5/0x3d0 fs/namei.c:3816
do_sys_openat2+0x12c/0x1c0 fs/open.c:1419
do_sys_open fs/open.c:1434 [inline]
__do_sys_openat fs/open.c:1450 [inline]
__se_sys_openat fs/open.c:1445 [inline]
__x64_sys_openat+0x139/0x160 fs/open.c:1445
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
-> #1 (&sbi->pipe_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x129/0xcc0 kernel/locking/mutex.c:747
autofs_write fs/autofs/waitq.c:55 [inline]
autofs_notify_daemon+0x6ec/0xdc0 fs/autofs/waitq.c:164
autofs_wait+0x1021/0x1a40 fs/autofs/waitq.c:426
autofs_mount_wait+0x16b/0x320 fs/autofs/root.c:255
autofs_d_automount+0x392/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1370 [inline]
__traverse_mounts+0x2fa/0x5a0 fs/namei.c:1415
traverse_mounts fs/namei.c:1444 [inline]
handle_mounts fs/namei.c:1547 [inline]
step_into+0x526/0xf10 fs/namei.c:1840
lookup_last fs/namei.c:2459 [inline]
path_lookupat+0x169/0x440 fs/namei.c:2483
filename_lookup+0x1f4/0x510 fs/namei.c:2512
kern_path+0x35/0x50 fs/namei.c:2610
lookup_bdev+0xc1/0x280 block/bdev.c:976
resume_store+0x16a/0x450 kernel/power/hibernate.c:1187
kernfs_fop_write_iter+0x37d/0x4d0 fs/kernfs/file.c:334
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x43b/0x940 fs/read_write.c:584
ksys_write+0x147/0x250 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
-> #0 (&of->mutex){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x129/0xcc0 kernel/locking/mutex.c:747
kernfs_fop_write_iter+0x1e9/0x4d0 fs/kernfs/file.c:325
do_iter_readv_writev fs/read_write.c:-1 [inline]
do_iter_write+0x79a/0xc70 fs/read_write.c:860
iter_file_splice_write+0x66f/0xc50 fs/splice.c:736
do_splice_from fs/splice.c:933 [inline]
do_splice+0xef0/0x1bf0 fs/splice.c:1292
__do_splice fs/splice.c:1370 [inline]
__do_sys_splice fs/splice.c:1586 [inline]
__se_sys_splice+0x37a/0x470 fs/splice.c:1568
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
other info that might help us debug this:
Chain exists of:
&of->mutex --> &sbi->pipe_mutex --> &pipe->mutex/1
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&pipe->mutex/1);
lock(&sbi->pipe_mutex);
lock(&pipe->mutex/1);
lock(&of->mutex);
*** DEADLOCK ***
2 locks held by syz.2.15109/16283:
#0: ffff88807bafa418 (sb_writers#11){.+.+}-{0:0}, at: __do_splice fs/splice.c:1370 [inline]
#0: ffff88807bafa418 (sb_writers#11){.+.+}-{0:0}, at: __do_sys_splice fs/splice.c:1586 [inline]
#0: ffff88807bafa418 (sb_writers#11){.+.+}-{0:0}, at: __se_sys_splice+0x37a/0x470 fs/splice.c:1568
#1: ffff888051ae1068 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x1a0/0xc50 fs/splice.c:683
stack backtrace:
CPU: 1 PID: 16283 Comm: syz.2.15109 Not tainted 6.6.102-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
<TASK>
dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
check_noncircular+0x2bd/0x3c0 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x129/0xcc0 kernel/locking/mutex.c:747
kernfs_fop_write_iter+0x1e9/0x4d0 fs/kernfs/file.c:325
do_iter_readv_writev fs/read_write.c:-1 [inline]
do_iter_write+0x79a/0xc70 fs/read_write.c:860
iter_file_splice_write+0x66f/0xc50 fs/splice.c:736
do_splice_from fs/splice.c:933 [inline]
do_splice+0xef0/0x1bf0 fs/splice.c:1292
__do_splice fs/splice.c:1370 [inline]
__do_sys_splice fs/splice.c:1586 [inline]
__se_sys_splice+0x37a/0x470 fs/splice.c:1568
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb25cb8ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb25d93b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007fb25cdb5fa0 RCX: 00007fb25cb8ebe9
RDX: 0000000000000006 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fb25cc11e19 R08: 0000000000000047 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb25cdb6038 R14: 00007fb25cdb5fa0 R15: 00007ffe80892a18
</TASK>
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
syzbot found the following issue on:
HEAD commit: bb9c90ab9c5a Linux 6.6.102
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1486cfbc580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7b989b97a0687b0a
dashboard link: https://syzkaller.appspot.com/bug?extid=91b0074eab4a94ac90ae
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/44e2224124c3/disk-bb9c90ab.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/33e0aef7ff42/vmlinux-bb9c90ab.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0515bc436228/bzImage-bb9c90ab.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+91b007...@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
6.6.102-syzkaller #0 Not tainted
------------------------------------------------------
syz.2.15109/16283 is trying to acquire lock:
ffff88805e870088 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1e9/0x4d0 fs/kernfs/file.c:325
but task is already holding lock:
ffff888051ae1068 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x1a0/0xc50 fs/splice.c:683
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&pipe->mutex/1){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x129/0xcc0 kernel/locking/mutex.c:747
__pipe_lock fs/pipe.c:103 [inline]
pipe_write+0x1c7/0x1af0 fs/pipe.c:444
__kernel_write_iter+0x274/0x670 fs/read_write.c:517
__kernel_write+0xf0/0x140 fs/read_write.c:537
autofs_write fs/autofs/waitq.c:57 [inline]
autofs_notify_daemon+0x6ff/0xdc0 fs/autofs/waitq.c:164
autofs_wait+0x1021/0x1a40 fs/autofs/waitq.c:426
autofs_mount_wait+0x16b/0x320 fs/autofs/root.c:255
autofs_d_automount+0x392/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1370 [inline]
__traverse_mounts+0x2fa/0x5a0 fs/namei.c:1415
traverse_mounts fs/namei.c:1444 [inline]
handle_mounts fs/namei.c:1547 [inline]
step_into+0x526/0xf10 fs/namei.c:1840
open_last_lookups fs/namei.c:3579 [inline]
path_openat+0x16bb/0x3190 fs/namei.c:3786
do_filp_open+0x1c5/0x3d0 fs/namei.c:3816
do_sys_openat2+0x12c/0x1c0 fs/open.c:1419
do_sys_open fs/open.c:1434 [inline]
__do_sys_openat fs/open.c:1450 [inline]
__se_sys_openat fs/open.c:1445 [inline]
__x64_sys_openat+0x139/0x160 fs/open.c:1445
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
-> #1 (&sbi->pipe_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x129/0xcc0 kernel/locking/mutex.c:747
autofs_write fs/autofs/waitq.c:55 [inline]
autofs_notify_daemon+0x6ec/0xdc0 fs/autofs/waitq.c:164
autofs_wait+0x1021/0x1a40 fs/autofs/waitq.c:426
autofs_mount_wait+0x16b/0x320 fs/autofs/root.c:255
autofs_d_automount+0x392/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1370 [inline]
__traverse_mounts+0x2fa/0x5a0 fs/namei.c:1415
traverse_mounts fs/namei.c:1444 [inline]
handle_mounts fs/namei.c:1547 [inline]
step_into+0x526/0xf10 fs/namei.c:1840
lookup_last fs/namei.c:2459 [inline]
path_lookupat+0x169/0x440 fs/namei.c:2483
filename_lookup+0x1f4/0x510 fs/namei.c:2512
kern_path+0x35/0x50 fs/namei.c:2610
lookup_bdev+0xc1/0x280 block/bdev.c:976
resume_store+0x16a/0x450 kernel/power/hibernate.c:1187
kernfs_fop_write_iter+0x37d/0x4d0 fs/kernfs/file.c:334
call_write_iter include/linux/fs.h:2018 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x43b/0x940 fs/read_write.c:584
ksys_write+0x147/0x250 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
-> #0 (&of->mutex){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x129/0xcc0 kernel/locking/mutex.c:747
kernfs_fop_write_iter+0x1e9/0x4d0 fs/kernfs/file.c:325
do_iter_readv_writev fs/read_write.c:-1 [inline]
do_iter_write+0x79a/0xc70 fs/read_write.c:860
iter_file_splice_write+0x66f/0xc50 fs/splice.c:736
do_splice_from fs/splice.c:933 [inline]
do_splice+0xef0/0x1bf0 fs/splice.c:1292
__do_splice fs/splice.c:1370 [inline]
__do_sys_splice fs/splice.c:1586 [inline]
__se_sys_splice+0x37a/0x470 fs/splice.c:1568
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
other info that might help us debug this:
Chain exists of:
&of->mutex --> &sbi->pipe_mutex --> &pipe->mutex/1
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&pipe->mutex/1);
lock(&sbi->pipe_mutex);
lock(&pipe->mutex/1);
lock(&of->mutex);
*** DEADLOCK ***
2 locks held by syz.2.15109/16283:
#0: ffff88807bafa418 (sb_writers#11){.+.+}-{0:0}, at: __do_splice fs/splice.c:1370 [inline]
#0: ffff88807bafa418 (sb_writers#11){.+.+}-{0:0}, at: __do_sys_splice fs/splice.c:1586 [inline]
#0: ffff88807bafa418 (sb_writers#11){.+.+}-{0:0}, at: __se_sys_splice+0x37a/0x470 fs/splice.c:1568
#1: ffff888051ae1068 (&pipe->mutex/1){+.+.}-{3:3}, at: iter_file_splice_write+0x1a0/0xc50 fs/splice.c:683
stack backtrace:
CPU: 1 PID: 16283 Comm: syz.2.15109 Not tainted 6.6.102-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
<TASK>
dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
check_noncircular+0x2bd/0x3c0 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
lock_acquire+0x197/0x410 kernel/locking/lockdep.c:5754
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x129/0xcc0 kernel/locking/mutex.c:747
kernfs_fop_write_iter+0x1e9/0x4d0 fs/kernfs/file.c:325
do_iter_readv_writev fs/read_write.c:-1 [inline]
do_iter_write+0x79a/0xc70 fs/read_write.c:860
iter_file_splice_write+0x66f/0xc50 fs/splice.c:736
do_splice_from fs/splice.c:933 [inline]
do_splice+0xef0/0x1bf0 fs/splice.c:1292
__do_splice fs/splice.c:1370 [inline]
__do_sys_splice fs/splice.c:1586 [inline]
__se_sys_splice+0x37a/0x470 fs/splice.c:1568
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb25cb8ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb25d93b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007fb25cdb5fa0 RCX: 00007fb25cb8ebe9
RDX: 0000000000000006 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fb25cc11e19 R08: 0000000000000047 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb25cdb6038 R14: 00007fb25cdb5fa0 R15: 00007ffe80892a18
</TASK>
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
syzbot
Dec 5, 2025, 4:08:15 PM12/5/25
to syzkaller...@googlegroups.com
Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.
Crashes did not happen for a while, no reproducer and no activity.
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