[moderation] [serial?] KCSAN: data-race in __stop_tty / pty_write_room (13)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7be4bc52fd9e Merge tag 'driver-core-7.4-rc1' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=122b4d0d580000
kernel config: https://syzkaller.appspot.com/x/.config?x=94ba7cc23030a212
dashboard link: https://syzkaller.appspot.com/bug?extid=b80089f747a307017a6c
compiler: Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
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/a514521acc9d/disk-7be4bc52.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/72070139a87b/vmlinux-7be4bc52.xz
kernel image: https://storage.googleapis.com/syzbot-assets/de33e63b138b/bzImage-7be4bc52.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b80089...@syzkaller.appspotmail.com

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

write to 0xffff88811a110d94 of 1 bytes by task 9425 on cpu 0:
__stop_tty+0x36/0x90 drivers/tty/tty_io.c:746
n_tty_ioctl_helper+0x2d1/0x370 drivers/tty/tty_ioctl.c:951
n_tty_ioctl+0x101/0x200 drivers/tty/n_tty.c:2496
tty_ioctl+0x843/0xbc0 drivers/tty/tty_io.c:2791
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x239d/0x2550 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a110d94 of 1 bytes by task 364 on cpu 1:
pty_write_room+0x19/0x70 drivers/tty/pty.c:129
tty_write_room+0x3f/0x60 drivers/tty/tty_ioctl.c:69
__process_echoes+0x36/0x6b0 drivers/tty/n_tty.c:683
flush_echoes drivers/tty/n_tty.c:785 [inline]
__receive_buf drivers/tty/n_tty.c:1618 [inline]
n_tty_receive_buf_common+0x90f/0xc10 drivers/tty/n_tty.c:1715
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1759
tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:394
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:452 [inline]
flush_to_ldisc+0x13a/0x320 drivers/tty/tty_buffer.c:502
process_one_work kernel/workqueue.c:3396 [inline]
process_scheduled_works+0x53f/0xa10 kernel/workqueue.c:3479
worker_thread+0x569/0x750 kernel/workqueue.c:3560
kthread+0x223/0x270 kernel/kthread.c:436
ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
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: 364 Comm: kworker/u8:6 Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
Workqueue: events_unbound flush_to_ldisc
==================================================================


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