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BUG: KCSAN: data-race in serial8250_do_startup / serial8250_modem_status

write to 0xffffffff893ddc86 of 1 bytes by task 18948 on cpu 1:
 serial8250_do_startup+0x15fb/0x1d30 drivers/tty/serial/8250/8250_port.c:2334
 serial8250_startup+0x41/0x50 drivers/tty/serial/8250/8250_port.c:2354
 uart_port_startup drivers/tty/serial/serial_core.c:321 [inline]
 uart_startup+0x464/0xac0 drivers/tty/serial/serial_core.c:365
 uart_port_activate+0x67/0xc0 drivers/tty/serial/serial_core.c:1949
 tty_port_open+0x16b/0x220 drivers/tty/tty_port.c:769
 uart_open+0x30/0x40 drivers/tty/serial/serial_core.c:1929
 tty_open+0x3d4/0xaf0 drivers/tty/tty_io.c:2137
 chrdev_open+0x2eb/0x3a0 fs/char_dev.c:411
 do_dentry_open+0x4be/0xa90 fs/open.c:947
 vfs_open+0x37/0x1e0 fs/open.c:1079
 do_open fs/namei.c:4699 [inline]
 path_openat+0x1b70/0x2050 fs/namei.c:4858
 do_file_open+0x16c/0x290 fs/namei.c:4887
 do_sys_openat2+0x94/0x130 fs/open.c:1364
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1381
 x64_sys_call+0x1e39/0x3020 arch/x86/include/generated/asm/syscalls_64.h:258
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffffff893ddc86 of 1 bytes by interrupt on cpu 0:
 serial8250_modem_status+0x6a/0x1e0 drivers/tty/serial/8250/8250_port.c:1742
 serial8250_handle_irq_locked+0x331/0x420 drivers/tty/serial/8250/8250_port.c:1822
 serial8250_handle_irq+0xaa/0x260 drivers/tty/serial/8250/8250_port.c:1841
 serial8250_default_handle_irq+0x8e/0x150 drivers/tty/serial/8250/8250_port.c:1855
 serial8250_interrupt+0x63/0x110 drivers/tty/serial/8250/8250_core.c:86
 __handle_irq_event_percpu+0x8b/0x480 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+0x154/0x450 kernel/irq/chip.c:856
 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
 vc_con_write_normal drivers/tty/vt/vt.c:3195 [inline]
 do_con_write+0x915/0x2d40 drivers/tty/vt/vt.c:3328
 con_write+0x25/0x1d0 drivers/tty/vt/vt.c:3660
 process_output_block drivers/tty/n_tty.c:557 [inline]
 n_tty_write+0x826/0xb80 drivers/tty/n_tty.c:2366
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write+0x378/0x680 drivers/tty/tty_io.c:1081
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x5a6/0x9f0 fs/read_write.c:688
 ksys_write+0xdc/0x1a0 fs/read_write.c:740
 __do_sys_write fs/read_write.c:751 [inline]
 __se_sys_write fs/read_write.c:748 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:748
 x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 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: 18924 Comm: syz.1.2897 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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