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BUG: KCSAN: data-race in serial8250_do_startup / serial8250_handle_irq

write to 0xffffffff88e89ac6 of 1 bytes by task 13827 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_handle_irq+0x3f9/0x660 drivers/tty/serial/8250/8250_port.c:1834
 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
 check_access kernel/kcsan/core.c:787 [inline]
 __tsan_unaligned_volatile_read8+0x132/0x190 kernel/kcsan/core.c:1086
 constant_test_bit arch/x86/include/asm/bitops.h:206 [inline]
 arch_test_bit arch/x86/include/asm/bitops.h:238 [inline]
 _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:142 [inline]
 folio_test_head include/linux/page-flags.h:843 [inline]
 folio_test_large include/linux/page-flags.h:864 [inline]
 folio_mapcount include/linux/mm.h:1141 [inline]
 zap_present_folio_ptes mm/memory.c:1525 [inline]
 zap_present_ptes mm/memory.c:1581 [inline]
 do_zap_pte_range mm/memory.c:1682 [inline]
 zap_pte_range mm/memory.c:1726 [inline]
 zap_pmd_range mm/memory.c:1818 [inline]
 zap_pud_range mm/memory.c:1847 [inline]
 zap_p4d_range mm/memory.c:1868 [inline]
 unmap_page_range+0x1563/0x2680 mm/memory.c:1889
 unmap_single_vma mm/memory.c:1932 [inline]
 unmap_vmas+0x23d/0x3a0 mm/memory.c:1976
 exit_mmap+0x1b0/0x6c0 mm/mmap.c:1280
 __mmput+0x28/0x1c0 kernel/fork.c:1129
 mmput+0x40/0x50 kernel/fork.c:1152
 exit_mm+0xe4/0x190 kernel/exit.c:582
 do_exit+0x417/0x15c0 kernel/exit.c:949
 do_group_exit+0xff/0x140 kernel/exit.c:1102
 get_signal+0xe59/0xf70 kernel/signal.c:3034
 arch_do_signal_or_restart+0x96/0x480 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x7a/0x100 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00 -> 0x05

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 13826 Comm: syz.0.3518 Not tainted 6.16.0-syzkaller-12063-g37816488247d #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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