[moderation] [serial?] KCSAN: data-race in __stop_tty / pty_write_room (9)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 37816488247d Merge tag 'net-6.17-rc1' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12bcbea2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7136549ecfde7285
dashboard link: https://syzkaller.appspot.com/bug?extid=bdece5d321692e086e81
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
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/e0a9a1ca014a/disk-37816488.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/92458dccfe6d/vmlinux-37816488.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5422a32a7400/bzImage-37816488.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bdece5...@syzkaller.appspotmail.com

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

write to 0xffff888136c9e9bc of 1 bytes by task 16736 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+0x842/0xb80 drivers/tty/tty_io.c:2801
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:598 [inline]
__se_sys_ioctl+0xcb/0x140 fs/ioctl.c:584
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:584
x64_sys_call+0x1816/0x2ff0 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 0xffff888136c9e9bc of 1 bytes by task 5085 on cpu 1:
pty_write_room+0x19/0x70 drivers/tty/pty.c:131
tty_write_room+0x3f/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+0x148/0x340 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3319
worker_thread+0x582/0x770 kernel/workqueue.c:3400
kthread+0x486/0x510 kernel/kthread.c:463
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: 5085 Comm: kworker/u8:51 Not tainted 6.16.0-syzkaller-12063-g37816488247d #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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.