KCSAN: data-race in serial8250_do_startup / serial8250_modem

Kernel	Title	Rank 🛈	Repro	Cause bisect	Fix bisect	Count	Last	Reported	Patched	Status
upstream	KCSAN: data-race in serial8250_do_startup / serial8250_modem_status (2) serial	6				1	72d	72d	0/29	auto-obsoleted due to no activity on 2025/12/17 04:14
upstream	KCSAN: data-race in serial8250_do_startup / serial8250_modem_status serial	6				5	132d	205d	0/29	auto-obsoleted due to no activity on 2025/10/18 03:59

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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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