[moderation] [serial?] KCSAN: data-race in do_con_write / stop_tty (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ae388edd4a8f Merge tag 'landlock-6.17-rc1' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d0c4a2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4274db12849c5e97
dashboard link: https://syzkaller.appspot.com/bug?extid=e4dc02bc10b806a1ec86
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/f5e365cd3574/disk-ae388edd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/63bbdda03237/vmlinux-ae388edd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fe98e3aba4a1/bzImage-ae388edd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e4dc02...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_con_write / stop_tty

write to 0xffff88811f590dbc of 1 bytes by task 30072 on cpu 1:
__stop_tty drivers/tty/tty_io.c:744 [inline]
stop_tty+0x4d/0xb0 drivers/tty/tty_io.c:766
n_tty_receive_char_flow_ctrl+0xec/0x1a0 drivers/tty/n_tty.c:1238
n_tty_receive_char_special drivers/tty/n_tty.c:1343 [inline]
n_tty_receive_buf_standard+0x4d2/0x2f10 drivers/tty/n_tty.c:1588
__receive_buf drivers/tty/n_tty.c:1624 [inline]
n_tty_receive_buf_common+0x805/0xbe0 drivers/tty/n_tty.c:1723
n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1763
tiocsti+0x170/0x1d0 drivers/tty/tty_io.c:2290
tty_ioctl+0x4a4/0xb80 drivers/tty/tty_io.c:2706
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 0xffff88811f590dbc of 1 bytes by task 30065 on cpu 0:
do_con_write+0x16b2/0x2940 drivers/tty/vt/vt.c:3154
con_write+0x24/0x40 drivers/tty/vt/vt.c:3516
process_output_block drivers/tty/n_tty.c:561 [inline]
n_tty_write+0x7d8/0xb10 drivers/tty/n_tty.c:2377
iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
file_tty_write+0x38c/0x670 drivers/tty/tty_io.c:1081
tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x49d/0x8e0 fs/read_write.c:686
ksys_write+0xda/0x1a0 fs/read_write.c:738
__do_sys_write fs/read_write.c:749 [inline]
__se_sys_write fs/read_write.c:746 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:746
x64_sys_call+0x27fe/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:2
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

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 30065 Comm: syz.4.9161 Tainted: G W 6.16.0-syzkaller-01056-gae388edd4a8f #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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[syzbot]

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