[moderation] [serial?] KCSAN: data-race in serial8250_tx_chars / stop_tty

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: bbeb83d3182a Merge tag 'kbuild-fixes-7.0-3' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1471d6da580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3a78dd265deac3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=c32840424eaed79e8828
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/3fe2f0f921b2/disk-bbeb83d3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ea4c0701d2e5/vmlinux-bbeb83d3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3bd84588d116/bzImage-bbeb83d3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c32840...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in serial8250_tx_chars / stop_tty

write to 0xffff8881060749bc of 1 bytes by task 2269 on cpu 1:
__stop_tty drivers/tty/tty_io.c:744 [inline]
stop_tty+0x4d/0xe0 drivers/tty/tty_io.c:766
n_tty_receive_char_flow_ctrl drivers/tty/n_tty.c:1230 [inline]
n_tty_receive_char_special drivers/tty/n_tty.c:1335 [inline]
n_tty_receive_buf_standard+0x691/0x3f60 drivers/tty/n_tty.c:1580
__receive_buf drivers/tty/n_tty.c:1616 [inline]
n_tty_receive_buf_common+0x7f3/0xc10 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:3276 [inline]
process_scheduled_works+0x513/0xa10 kernel/workqueue.c:3359
worker_thread+0x58a/0x780 kernel/workqueue.c:3440
kthread+0x22a/0x280 kernel/kthread.c:436
ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff8881060749bc of 1 bytes by interrupt on cpu 0:
uart_tx_stopped include/linux/serial_core.h:1149 [inline]
serial8250_tx_chars+0x85/0x490 drivers/tty/serial/8250/8250_port.c:1681
serial8250_handle_irq_locked+0x3c0/0x420 drivers/tty/serial/8250/8250_port.c:1825
serial8250_handle_irq+0xad/0x280 drivers/tty/serial/8250/8250_port.c:1841
serial8250_default_handle_irq+0x8e/0x170 drivers/tty/serial/8250/8250_port.c:1855
serial8250_interrupt+0x63/0x130 drivers/tty/serial/8250/8250_core.c:86
__handle_irq_event_percpu+0x9c/0x4d0 kernel/irq/handle.c:209
handle_irq_event_percpu kernel/irq/handle.c:246 [inline]
handle_irq_event+0x64/0xf0 kernel/irq/handle.c:263
handle_edge_irq+0x154/0x470 kernel/irq/chip.c:855
generic_handle_irq_desc include/linux/irqdesc.h:186 [inline]
handle_irq arch/x86/kernel/irq.c:262 [inline]
call_irq_handler arch/x86/kernel/irq.c:-1 [inline]
__common_interrupt+0x60/0xb0 arch/x86/kernel/irq.c:333
common_interrupt+0x7e/0x90 arch/x86/kernel/irq.c:326
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
__sanitizer_cov_trace_const_cmp4+0x0/0x90 kernel/kcov.c:309
do_recvmmsg+0x285/0x560 net/socket.c:2959
__sys_recvmmsg net/socket.c:3023 [inline]
__do_sys_recvmmsg net/socket.c:3046 [inline]
__se_sys_recvmmsg net/socket.c:3039 [inline]
__x64_sys_recvmmsg+0xe5/0x170 net/socket.c:3039
x64_sys_call+0x80f/0x3020 arch/x86/include/generated/asm/syscalls_64.h:300
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 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: 5139 Comm: syz.1.428 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


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