[moderation] [serial?] KCSAN: data-race in serial8250_do_startup / serial8250_modem_status (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 552c50713f27 Merge tag 'vfio-v6.18-rc3' of https://github...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=165fc3cd980000
kernel config: https://syzkaller.appspot.com/x/.config?x=a763affcb14f3d17
dashboard link: https://syzkaller.appspot.com/bug?extid=3ad2b8f47210309e2231
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/3bf912922a69/disk-552c5071.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f7475d2ef8c4/vmlinux-552c5071.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dbbcd51deeb7/bzImage-552c5071.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3ad2b8...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in serial8250_do_startup / serial8250_modem_status

write to 0xffffffff890d8e66 of 1 bytes by task 9550 on cpu 1:
serial8250_do_startup+0x1491/0x1c10 drivers/tty/serial/8250/8250_port.c:2327
serial8250_startup+0x41/0x50 drivers/tty/serial/8250/8250_port.c:2347
uart_port_startup drivers/tty/serial/serial_core.c:321 [inline]
uart_startup+0x468/0x8e0 drivers/tty/serial/serial_core.c:365
uart_port_activate+0x67/0xc0 drivers/tty/serial/serial_core.c:1974
tty_port_open+0x196/0x270 drivers/tty/tty_port.c:747
uart_open+0x30/0x40 drivers/tty/serial/serial_core.c:1954
tty_open+0x3d4/0xaf0 drivers/tty/tty_io.c:2137
chrdev_open+0x2eb/0x3a0 fs/char_dev.c:414
do_dentry_open+0x649/0xa20 fs/open.c:965
vfs_open+0x37/0x1e0 fs/open.c:1097
do_open fs/namei.c:3975 [inline]
path_openat+0x1c5e/0x2170 fs/namei.c:4134
do_filp_open+0x109/0x230 fs/namei.c:4161
do_sys_openat2+0xa6/0x110 fs/open.c:1437
do_sys_open fs/open.c:1452 [inline]
__do_sys_openat fs/open.c:1468 [inline]
__se_sys_openat fs/open.c:1463 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1463
x64_sys_call+0x2eab/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
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 0xffffffff890d8e66 of 1 bytes by interrupt on cpu 0:
serial8250_modem_status+0x6a/0x1e0 drivers/tty/serial/8250/8250_port.c:1740
serial8250_handle_irq+0x3d6/0x660 drivers/tty/serial/8250/8250_port.c:1824
serial8250_default_handle_irq+0x8e/0x170 drivers/tty/serial/8250/8250_port.c:1846
serial8250_interrupt+0x63/0x130 drivers/tty/serial/8250/8250_core.c:82
__handle_irq_event_percpu+0x9d/0x540 kernel/irq/handle.c:203
handle_irq_event_percpu kernel/irq/handle.c:240 [inline]
handle_irq_event+0x64/0xf0 kernel/irq/handle.c:257
handle_edge_irq+0x154/0x470 kernel/irq/chip.c:855
generic_handle_irq_desc include/linux/irqdesc.h:173 [inline]
handle_irq arch/x86/kernel/irq.c:254 [inline]
call_irq_handler arch/x86/kernel/irq.c:-1 [inline]
__common_interrupt+0x60/0xb0 arch/x86/kernel/irq.c:325
common_interrupt+0x3e/0x90 arch/x86/kernel/irq.c:318
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
native_irq_enable arch/x86/include/asm/irqflags.h:-1 [inline]
arch_local_irq_enable arch/x86/include/asm/irqflags.h:119 [inline]
handle_softirqs+0x6d/0x290 kernel/softirq.c:606
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0x3a/0xc0 kernel/softirq.c:723
common_interrupt+0x83/0x90 arch/x86/kernel/irq.c:318
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
finish_task_switch+0xb6/0x2b0 kernel/sched/core.c:5193
context_switch kernel/sched/core.c:5328 [inline]
__schedule+0x6b9/0xb30 kernel/sched/core.c:6929
__schedule_loop kernel/sched/core.c:7011 [inline]
schedule+0x5f/0xd0 kernel/sched/core.c:7026
do_nanosleep+0x96/0x330 kernel/time/hrtimer.c:2116
hrtimer_nanosleep+0xdd/0x280 kernel/time/hrtimer.c:2163
common_nsleep+0x62/0x80 kernel/time/posix-timers.c:1352
__do_sys_clock_nanosleep kernel/time/posix-timers.c:1398 [inline]
__se_sys_clock_nanosleep+0x21a/0x250 kernel/time/posix-timers.c:1375
__x64_sys_clock_nanosleep+0x55/0x70 kernel/time/posix-timers.c:1375
x64_sys_call+0x2731/0x3000 arch/x86/include/generated/asm/syscalls_64.h:231
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 -> 0x05

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 9548 Comm: syz.0.1439 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup