[moderation] [serial?] KCSAN: data-race in pty_write / tty_send_xchar (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 023777797472 Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15c6c1b2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=b22754c9158592d54fb9
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/7a5f13477745/disk-02377779.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/526049e9cfef/vmlinux-02377779.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1da969a6e6f0/bzImage-02377779.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b22754...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in pty_write / tty_send_xchar

write to 0xffff88814c0055bc of 1 bytes by task 11160 on cpu 0:
__stop_tty drivers/tty/tty_io.c:744 [inline]
stop_tty drivers/tty/tty_io.c:766 [inline]
tty_send_xchar+0x1c8/0x2b0 drivers/tty/tty_io.c:1156
n_tty_ioctl_helper+0x2a9/0x370 drivers/tty/tty_ioctl.c:-1
n_tty_ioctl+0x101/0x230 drivers/tty/n_tty.c:2496
tty_ioctl+0x83e/0xb80 drivers/tty/tty_io.c:2801
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+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88814c0055bc of 1 bytes by task 58 on cpu 1:
pty_write+0x24/0x90 drivers/tty/pty.c:113
tty_put_char+0x8f/0xc0 drivers/tty/tty_io.c:3154
n_tty_process_echo_ops drivers/tty/n_tty.c:643 [inline]
__process_echoes+0x2f9/0x6b0 drivers/tty/n_tty.c:689
flush_echoes drivers/tty/n_tty.c:785 [inline]
__receive_buf drivers/tty/n_tty.c:1618 [inline]
n_tty_receive_buf_common+0x918/0xc10 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: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:3257 [inline]
process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
worker_thread+0x6bc/0x8b0 kernel/workqueue.c:3421
kthread+0x488/0x510 kernel/kthread.c:463
ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 58 Comm: kworker/u8:4 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events_unbound flush_to_ldisc
==================================================================


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