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BUG: KCSAN: data-race in serial8250_do_startup / serial8250_modem_status

write to 0xffffffff88e89ac6 of 1 bytes by task 25967 on cpu 1:
 serial8250_do_startup+0x13de/0x1b10 drivers/tty/serial/8250/8250_port.c:2366
 serial8250_startup+0x41/0x50 drivers/tty/serial/8250/8250_port.c:2388
 uart_port_startup drivers/tty/serial/serial_core.c:324 [inline]
 uart_startup+0x465/0x8e0 drivers/tty/serial/serial_core.c:368
 uart_port_activate+0x67/0xc0 drivers/tty/serial/serial_core.c:1993
 tty_port_open+0x148/0x1d0 drivers/tty/tty_port.c:763
 uart_open+0x30/0x40 drivers/tty/serial/serial_core.c:1973
 tty_open+0x3d4/0xaf0 drivers/tty/tty_io.c:2137
 chrdev_open+0x2eb/0x3a0 fs/char_dev.c:414
 do_dentry_open+0x646/0xa20 fs/open.c:965
 vfs_open+0x37/0x1e0 fs/open.c:1095
 do_open fs/namei.c:3887 [inline]
 path_openat+0x1c5e/0x2170 fs/namei.c:4046
 do_filp_open+0x109/0x230 fs/namei.c:4073
 do_sys_openat2+0xa6/0x110 fs/open.c:1435
 do_sys_open fs/open.c:1450 [inline]
 __do_sys_openat fs/open.c:1466 [inline]
 __se_sys_openat fs/open.c:1461 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1461
 x64_sys_call+0x2e9c/0x2ff0 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 0xffffffff88e89ac6 of 1 bytes by interrupt on cpu 0:
 serial8250_modem_status+0x6a/0x1e0 drivers/tty/serial/8250/8250_port.c:1749
 serial8250_handle_irq+0x3d6/0x660 drivers/tty/serial/8250/8250_port.c:1833
 serial8250_default_handle_irq+0x8e/0x140 drivers/tty/serial/8250/8250_port.c:1856
 serial8250_interrupt+0x60/0x110 drivers/tty/serial/8250/8250_core.c:82
 __handle_irq_event_percpu+0x90/0x440 kernel/irq/handle.c:158
 handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
 handle_irq_event+0x64/0xf0 kernel/irq/handle.c:210
 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:266 [inline]
 __common_interrupt+0x63/0x100 arch/x86/kernel/irq.c:292
 common_interrupt+0x7e/0x90 arch/x86/kernel/irq.c:285
 asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:693
 arch_static_branch arch/x86/include/asm/jump_label.h:36 [inline]
 trace_rss_stat include/trace/events/kmem.h:424 [inline]
 mm_trace_rss_stat mm/memory.c:181 [inline]
 inc_mm_counter include/linux/mm.h:2610 [inline]
 insert_page_into_pte_locked+0x3b4/0x640 mm/memory.c:2182
 insert_page+0x121/0x1a0 mm/memory.c:2203
 vm_insert_page+0x1d9/0x260 mm/memory.c:2354
 kcov_mmap+0xad/0x110 kernel/kcov.c:506
 vfs_mmap include/linux/fs.h:2289 [inline]
 mmap_file mm/internal.h:167 [inline]
 __mmap_new_file_vma mm/vma.c:2413 [inline]
 __mmap_new_vma mm/vma.c:2476 [inline]
 __mmap_region mm/vma.c:2669 [inline]
 mmap_region+0xfb0/0x1630 mm/vma.c:2739
 do_mmap+0x9b3/0xbe0 mm/mmap.c:558
 vm_mmap_pgoff+0x17a/0x2e0 mm/util.c:580
 ksys_mmap_pgoff+0x268/0x310 mm/mmap.c:604
 x64_sys_call+0x14a3/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:10
 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: 25958 Comm: syz.1.7224 Tainted: G        W           6.16.0-syzkaller-11852-g479058002c32 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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