[moderation] [serial?] KCSAN: data-race in __stop_tty / do_con_write (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b95f03f04d47 Merge tag 'mm-hotfixes-stable-2026-07-20-11-3..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=109512b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=84b3039e8461eef5
dashboard link: https://syzkaller.appspot.com/bug?extid=63b1e79c99354be9dcd8
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), 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/9cae06105b5f/disk-b95f03f0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dc7102a7ca7b/vmlinux-b95f03f0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/110e935b446f/bzImage-b95f03f0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+63b1e7...@syzkaller.appspotmail.com

netlink: 8 bytes leftover after parsing attributes in process `syz.3.1728'.
==================================================================
BUG: KCSAN: data-race in __stop_tty / do_con_write

write to 0xffff88811961ad94 of 1 bytes by task 10926 on cpu 0:
__stop_tty+0x36/0x90 drivers/tty/tty_io.c:744
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+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+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811961ad94 of 1 bytes by task 10914 on cpu 1:
do_con_write+0x1bd2/0x2a80 drivers/tty/vt/vt.c:3305
con_write+0x25/0x1d0 drivers/tty/vt/vt.c:3661
process_output_block drivers/tty/n_tty.c:557 [inline]
n_tty_write+0x7f4/0xb00 drivers/tty/n_tty.c:2366
iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
file_tty_write+0x397/0x690 drivers/tty/tty_io.c:1081
tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x57d/0x990 fs/read_write.c:687
ksys_write+0xdc/0x1a0 fs/read_write.c:739
__do_sys_write fs/read_write.c:750 [inline]
__se_sys_write fs/read_write.c:747 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:747
x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x136/0x3c0 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: 1 UID: 0 PID: 10914 Comm: syz.3.1728 Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================


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