[moderation] [serial?] KCSAN: data-race in n_tty_flush_buffer / n_tty_lookahead_flow_ctrl (9)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b7ff7151e653 Merge tag 'hwmon-for-v6.19-final' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13cd5144580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=80806cf7508e92c7cc86
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/2df8be7c64f3/disk-b7ff7151.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/73a4ffde1302/vmlinux-b7ff7151.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9058af9cc379/bzImage-b7ff7151.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+80806c...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_flush_buffer / n_tty_lookahead_flow_ctrl

read-write to 0xffffc9000729b270 of 8 bytes by task 5323 on cpu 0:
n_tty_lookahead_flow_ctrl+0x51/0x300 drivers/tty/n_tty.c:1483
tty_port_default_lookahead_buf+0x91/0xc0 drivers/tty/tty_port.c:59
lookahead_bufs drivers/tty/tty_buffer.c:428 [inline]
flush_to_ldisc+0x288/0x340 drivers/tty/tty_buffer.c:498
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

write to 0xffffc9000729b270 of 8 bytes by task 11199 on cpu 1:
reset_buffer_flags drivers/tty/n_tty.c:322 [inline]
n_tty_flush_buffer+0xa8/0x1d0 drivers/tty/n_tty.c:350
tty_ldisc_hangup+0x77/0x480 drivers/tty/tty_ldisc.c:699
__tty_hangup+0x3c2/0x540 drivers/tty/tty_io.c:621
tty_vhangup+0x17/0x20 drivers/tty/tty_io.c:691
pty_close+0x2c5/0x2f0 drivers/tty/pty.c:77
tty_release+0x1ff/0xb10 drivers/tty/tty_io.c:1745
__fput+0x29b/0x650 fs/file_table.c:468
____fput+0x1c/0x30 fs/file_table.c:496
task_work_run+0x130/0x1a0 kernel/task_work.c:233
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x466/0x1590 kernel/exit.c:971
do_group_exit+0xfe/0x140 kernel/exit.c:1112
get_signal+0xe4f/0xf60 kernel/signal.c:3034
arch_do_signal_or_restart+0x96/0x450 arch/x86/kernel/signal.c:337
__exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
exit_to_user_mode_loop+0x6a/0x6f0 kernel/entry/common.c:75
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
do_syscall_64+0x1d3/0x2a0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000801 -> 0x0000000000001001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 11199 Comm: syz.2.1559 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================


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