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BUG: KCSAN: data-race in n_tty_flush_buffer / n_tty_poll

read to 0xffffc900107e5260 of 8 bytes by task 4019 on cpu 1:
 input_available_p drivers/tty/n_tty.c:1913 [inline]
 n_tty_poll+0x2a8/0x450 drivers/tty/n_tty.c:2444
 tty_poll+0x79/0xf0 drivers/tty/tty_io.c:2199
 vfs_poll include/linux/poll.h:82 [inline]
 do_pollfd fs/select.c:866 [inline]
 do_poll fs/select.c:909 [inline]
 do_sys_poll+0x698/0xc10 fs/select.c:1004
 __do_sys_poll fs/select.c:1066 [inline]
 __se_sys_poll fs/select.c:1054 [inline]
 __x64_sys_poll+0x12c/0x230 fs/select.c:1054
 x64_sys_call+0x2891/0x3020 arch/x86/include/generated/asm/syscalls_64.h:8
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffffc900107e5260 of 16 bytes by task 4011 on cpu 0:
 reset_buffer_flags drivers/tty/n_tty.c:316 [inline]
 n_tty_flush_buffer+0x61/0x1d0 drivers/tty/n_tty.c:350
 tty_ldisc_hangup+0x77/0x480 drivers/tty/tty_ldisc.c:699
 __tty_hangup+0x3c2/0x540 drivers/tty/tty_io.c:621
 tty_vhangup+0x17/0x20 drivers/tty/tty_io.c:691
 pty_close+0x2c5/0x2f0 drivers/tty/pty.c:77
 tty_release+0x1ff/0xb10 drivers/tty/tty_io.c:1745
 __fput+0x29b/0x650 fs/file_table.c:469
 ____fput+0x1c/0x30 fs/file_table.c:497
 task_work_run+0x130/0x1a0 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
 exit_to_user_mode_loop+0x1f4/0x6f0 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x249/0x370 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4011 Comm: syz.0.221 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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