[moderation] [serial?] KCSAN: data-race in __stop_tty / pty_write_room (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 27605c8c0f69 Merge tag 'net-6.16-rc2' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=159c7682580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f437300db311c188
dashboard link: https://syzkaller.appspot.com/bug?extid=e29a46595d0cc68c2849
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/6d038d85b6de/disk-27605c8c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1c64b4d84fa8/vmlinux-27605c8c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c1c2b0bdce9d/bzImage-27605c8c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e29a46...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __stop_tty / pty_write_room

write to 0xffff888119b86dbc of 1 bytes by task 6137 on cpu 0:
__stop_tty+0x36/0x90 drivers/tty/tty_io.c:744
n_tty_ioctl_helper+0x1e9/0x210 drivers/tty/tty_ioctl.c:951
n_tty_ioctl+0x101/0x200 drivers/tty/n_tty.c:2509
tty_ioctl+0x845/0xb80 drivers/tty/tty_io.c:2801
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:893
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893
x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888119b86dbc of 1 bytes by task 31 on cpu 1:
pty_write_room+0x19/0x70 drivers/tty/pty.c:131
tty_write_room+0x3c/0x60 drivers/tty/tty_ioctl.c:69
__process_echoes+0x36/0x6b0 drivers/tty/n_tty.c:687
flush_echoes drivers/tty/n_tty.c:791 [inline]
__receive_buf drivers/tty/n_tty.c:1626 [inline]
n_tty_receive_buf_common+0x8e4/0xbe0 drivers/tty/n_tty.c:1723
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1769
tty_ldisc_receive_buf+0x63/0xf0 drivers/tty/tty_buffer.c:387
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:445 [inline]
flush_to_ldisc+0x144/0x360 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3321
worker_thread+0x582/0x770 kernel/workqueue.c:3402
kthread+0x486/0x510 kernel/kthread.c:464
ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 31 Comm: kworker/u8:1 Not tainted 6.16.0-rc1-syzkaller-00101-g27605c8c0f69 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: events_unbound flush_to_ldisc
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.