[moderation] [serial?] KCSAN: data-race in serial8250_do_startup / serial8250_modem_status (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d26143bb38e2 Merge tag 'spi-fix-v6.19-rc2' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12825b92580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=3aef261f2643b65ab7d7
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/d9633a9e1613/disk-d26143bb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/682d036ffbf7/vmlinux-d26143bb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c65315bc62ce/bzImage-d26143bb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3aef26...@syzkaller.appspotmail.com

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

write to 0xffffffff88f0ddf6 of 1 bytes by task 2444 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:1946
tty_port_open+0x196/0x270 drivers/tty/tty_port.c:747
uart_open+0x30/0x40 drivers/tty/serial/serial_core.c:1926
tty_open+0x3d4/0xaf0 drivers/tty/tty_io.c:2137
chrdev_open+0x2eb/0x3a0 fs/char_dev.c:414
do_dentry_open+0x54b/0xa60 fs/open.c:962
vfs_open+0x37/0x1e0 fs/open.c:1094
do_open fs/namei.c:4628 [inline]
path_openat+0x1ddd/0x23b0 fs/namei.c:4787
do_filp_open+0x109/0x230 fs/namei.c:4814
do_sys_openat2+0xa6/0x150 fs/open.c:1430
do_sys_open fs/open.c:1436 [inline]
__do_sys_openat fs/open.c:1452 [inline]
__se_sys_openat fs/open.c:1447 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1447
x64_sys_call+0x2b07/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff88f0ddf6 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:86
__handle_irq_event_percpu+0x8b/0x4c0 kernel/irq/handle.c:211
handle_irq_event_percpu kernel/irq/handle.c:248 [inline]
handle_irq_event+0x64/0xf0 kernel/irq/handle.c:265
handle_edge_irq+0x154/0x470 kernel/irq/chip.c:855
generic_handle_irq_desc include/linux/irqdesc.h:172 [inline]
handle_irq arch/x86/kernel/irq.c:255 [inline]
call_irq_handler arch/x86/kernel/irq.c:-1 [inline]
__common_interrupt+0x60/0xb0 arch/x86/kernel/irq.c:326
common_interrupt+0x7e/0x90 arch/x86/kernel/irq.c:319
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688
smp_call_function_many_cond+0x8ad/0xc40 kernel/smp.c:872
on_each_cpu_cond_mask+0x3c/0x80 kernel/smp.c:1043
__flush_tlb_multi arch/x86/include/asm/paravirt.h:91 [inline]
flush_tlb_multi arch/x86/mm/tlb.c:1382 [inline]
flush_tlb_mm_range+0x21f/0x5c0 arch/x86/mm/tlb.c:1472
flush_tlb_page arch/x86/include/asm/tlbflush.h:324 [inline]
ptep_clear_flush+0xba/0xe0 mm/pgtable-generic.c:103
wp_page_copy mm/memory.c:3785 [inline]
do_wp_page+0x152a/0x2510 mm/memory.c:4180
handle_pte_fault mm/memory.c:6289 [inline]
__handle_mm_fault mm/memory.c:6411 [inline]
handle_mm_fault+0x7b0/0x2c60 mm/memory.c:6580
do_user_addr_fault+0x630/0x1080 arch/x86/mm/fault.c:1336
handle_page_fault arch/x86/mm/fault.c:1476 [inline]
exc_page_fault+0x62/0xa0 arch/x86/mm/fault.c:1532
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

value changed: 0x00 -> 0x05

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2438 Comm: syz.9.13970 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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