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BUG: KCSAN: data-race in start_tty / uart_write

write to 0xffff888138358dbc of 1 bytes by task 46 on cpu 0:
 __start_tty drivers/tty/tty_io.c:793 [inline]
 start_tty+0x81/0x170 drivers/tty/tty_io.c:815
 n_tty_receive_char+0xc0/0x6a0 drivers/tty/n_tty.c:1411
 n_tty_receive_buf_standard+0x3b3/0x3a30 drivers/tty/n_tty.c:1589
 __receive_buf drivers/tty/n_tty.c:1613 [inline]
 n_tty_receive_buf_common+0x72d/0xbf0 drivers/tty/n_tty.c:1711
 n_tty_receive_buf2+0x2e/0x40 drivers/tty/n_tty.c:1746
 tty_ldisc_receive_buf+0x5b/0xf0 drivers/tty/tty_buffer.c:457
 tty_port_default_receive_buf+0x54/0x80 drivers/tty/tty_port.c:39
 receive_buf drivers/tty/tty_buffer.c:515 [inline]
 flush_to_ldisc+0x1d9/0x470 drivers/tty/tty_buffer.c:565
 process_one_work+0x3d3/0x720 kernel/workqueue.c:2289
 worker_thread+0x618/0xa70 kernel/workqueue.c:2436
 kthread+0x1a9/0x1e0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30

read to 0xffff888138358dbc of 1 bytes by task 2624 on cpu 1:
 uart_tx_stopped include/linux/serial_core.h:774 [inline]
 __uart_start drivers/tty/serial/serial_core.c:140 [inline]
 uart_write+0x34e/0x5a0 drivers/tty/serial/serial_core.c:606
 process_output_block drivers/tty/n_tty.c:586 [inline]
 n_tty_write+0x809/0xb10 drivers/tty/n_tty.c:2350
 do_tty_write drivers/tty/tty_io.c:1024 [inline]
 file_tty_write+0x3f9/0x650 drivers/tty/tty_io.c:1095
 tty_write+0x24/0x30 drivers/tty/tty_io.c:1116
 do_iter_write+0x494/0x750 fs/read_write.c:855
 vfs_iter_write+0x4c/0x70 fs/read_write.c:896
 iter_file_splice_write+0x44a/0x7c0 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:931
 splice_direct_to_actor+0x305/0x620 fs/splice.c:886
 do_splice_direct+0xfb/0x180 fs/splice.c:974
 do_sendfile+0x3bf/0x910 fs/read_write.c:1249
 __do_sys_sendfile64 fs/read_write.c:1317 [inline]
 __se_sys_sendfile64 fs/read_write.c:1303 [inline]
 __x64_sys_sendfile64+0x10c/0x150 fs/read_write.c:1303
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x01 -> 0x00

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2624 Comm: syz-executor.5 Not tainted 6.0.0-rc6-syzkaller-00286-ga63f2e7cb110-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
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