serio: Serial port ptm0
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.3148/13704 is trying to acquire lock:
ffff8880686d62c0 (kn->active#976){++++}-{0:0}, at: kernfs_remove_by_name_ns+0x91/0x100 fs/kernfs/dir.c:1566

but task is already holding lock:
ffffffff8cf514a8 (serio_mutex){+.+.}-{3:3}, at: serio_unregister_port+0x2b/0x150 drivers/input/serio/serio.c:707

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (serio_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0x1e5/0x2400 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_interruptible_nested+0x17/0x20 kernel/locking/mutex.c:765
       drvctl_store+0x2a/0xae0 drivers/input/serio/serio.c:388
       kernfs_fop_write_iter+0x3a8/0x500 fs/kernfs/file.c:296
       call_write_iter include/linux/fs.h:2179 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0x748/0xd70 fs/read_write.c:594
       ksys_write+0x153/0x260 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (kn->active#976){++++}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x2c66/0x7b50 kernel/locking/lockdep.c:5012
       lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5625
       kernfs_drain fs/kernfs/dir.c:478 [inline]
       __kernfs_remove+0x5da/0xcb0 fs/kernfs/dir.c:1372
       kernfs_remove_by_name_ns+0x91/0x100 fs/kernfs/dir.c:1566
       kernfs_remove_by_name include/linux/kernfs.h:598 [inline]
       remove_files fs/sysfs/group.c:28 [inline]
       sysfs_remove_group+0xfd/0x290 fs/sysfs/group.c:289
       sysfs_remove_groups+0x50/0xa0 fs/sysfs/group.c:313
       device_remove_groups drivers/base/core.c:2498 [inline]
       device_remove_attrs+0xc2/0x140 drivers/base/core.c:2698
       device_del+0x637/0xa80 drivers/base/core.c:3614
       serio_destroy_port+0x34a/0x470 drivers/input/serio/serio.c:573
       serio_unregister_port+0x12c/0x150 drivers/input/serio/serio.c:709
       serport_ldisc_read+0x4ec/0x5b0 drivers/input/serio/serport.c:188
       iterate_tty_read drivers/tty/tty_io.c:868 [inline]
       tty_read+0x2af/0x5c0 drivers/tty/tty_io.c:944
       call_read_iter include/linux/fs.h:2173 [inline]
       aio_read+0x33a/0x490 fs/aio.c:1554
       __io_submit_one fs/aio.c:-1 [inline]
       io_submit_one+0x68b/0x1310 fs/aio.c:2013
       __do_sys_io_submit fs/aio.c:2072 [inline]
       __se_sys_io_submit+0x19d/0x310 fs/aio.c:2042
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(serio_mutex);
                               lock(kn->active#976);
                               lock(serio_mutex);
  lock(kn->active#976);

 *** DEADLOCK ***

2 locks held by syz.2.3148/13704:
 #0: ffff88806137a098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:252
 #1: ffffffff8cf514a8 (serio_mutex){+.+.}-{3:3}, at: serio_unregister_port+0x2b/0x150 drivers/input/serio/serio.c:707

stack backtrace:
CPU: 1 PID: 13704 Comm: syz.2.3148 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x2c66/0x7b50 kernel/locking/lockdep.c:5012
 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5625
 kernfs_drain fs/kernfs/dir.c:478 [inline]
 __kernfs_remove+0x5da/0xcb0 fs/kernfs/dir.c:1372
 kernfs_remove_by_name_ns+0x91/0x100 fs/kernfs/dir.c:1566
 kernfs_remove_by_name include/linux/kernfs.h:598 [inline]
 remove_files fs/sysfs/group.c:28 [inline]
 sysfs_remove_group+0xfd/0x290 fs/sysfs/group.c:289
 sysfs_remove_groups+0x50/0xa0 fs/sysfs/group.c:313
 device_remove_groups drivers/base/core.c:2498 [inline]
 device_remove_attrs+0xc2/0x140 drivers/base/core.c:2698
 device_del+0x637/0xa80 drivers/base/core.c:3614
 serio_destroy_port+0x34a/0x470 drivers/input/serio/serio.c:573
 serio_unregister_port+0x12c/0x150 drivers/input/serio/serio.c:709
 serport_ldisc_read+0x4ec/0x5b0 drivers/input/serio/serport.c:188
 iterate_tty_read drivers/tty/tty_io.c:868 [inline]
 tty_read+0x2af/0x5c0 drivers/tty/tty_io.c:944
 call_read_iter include/linux/fs.h:2173 [inline]
 aio_read+0x33a/0x490 fs/aio.c:1554
 __io_submit_one fs/aio.c:-1 [inline]
 io_submit_one+0x68b/0x1310 fs/aio.c:2013
 __do_sys_io_submit fs/aio.c:2072 [inline]
 __se_sys_io_submit+0x19d/0x310 fs/aio.c:2042
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f4051cb5159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f404ff0d028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d1
RAX: ffffffffffffffda RBX: 00007f4051f3cfa0 RCX: 00007f4051cb5159
RDX: 0000200000000140 RSI: 0000000000000002 RDI: 00007f404fe5e000
RBP: 00007f4051d4c06b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4051f3d038 R14: 00007f4051f3cfa0 R15: 00007fff72433708
 </TASK>