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BUG: KCSAN: data-race in n_tty_receive_char / n_tty_write

write to 0xffffc9000109b028 of 8 bytes by task 7247 on cpu 0:
 commit_echoes drivers/tty/n_tty.c:738 [inline]
 n_tty_receive_char+0x44e/0x6d0 drivers/tty/n_tty.c:1413
 n_tty_receive_buf_standard+0x563/0x3cb0 drivers/tty/n_tty.c:1582
 __receive_buf drivers/tty/n_tty.c:1616 [inline]
 n_tty_receive_buf_common+0x821/0xc10 drivers/tty/n_tty.c:1715
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1759
 tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:394
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:452 [inline]
 flush_to_ldisc+0x13a/0x330 drivers/tty/tty_buffer.c:502
 process_one_work kernel/workqueue.c:3387 [inline]
 process_scheduled_works+0x56a/0xa50 kernel/workqueue.c:3470
 worker_thread+0x569/0x750 kernel/workqueue.c:3551
 kthread+0x223/0x270 kernel/kthread.c:436
 ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffc9000109b028 of 8 bytes by task 15407 on cpu 1:
 process_echoes drivers/tty/n_tty.c:762 [inline]
 n_tty_write+0x178/0xb00 drivers/tty/n_tty.c:2352
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write+0x392/0x6a0 drivers/tty/tty_io.c:1054
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1075
 iter_file_splice_write+0x6a0/0xa60 fs/splice.c:736
 do_splice_from fs/splice.c:936 [inline]
 direct_splice_actor+0x158/0x280 fs/splice.c:1159
 splice_direct_to_actor+0x2f9/0x680 fs/splice.c:1103
 do_splice_direct_actor fs/splice.c:1202 [inline]
 do_splice_direct+0x119/0x1a0 fs/splice.c:1228
 do_sendfile+0x37d/0x640 fs/read_write.c:1371
 __do_sys_sendfile64 fs/read_write.c:1432 [inline]
 __se_sys_sendfile64 fs/read_write.c:1418 [inline]
 __x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1418
 x64_sys_call+0x1015/0x2550 arch/x86/include/generated/asm/syscalls_64.h:41
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000039 -> 0x000000000000003f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 15407 Comm: syz.4.3643 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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