syzbot

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BUG: KCSAN: data-race in __process_echoes / n_tty_write

write to 0xffffc900011bd280 of 8 bytes by task 51 on cpu 0:
 __process_echoes+0x63e/0x6b0 drivers/tty/n_tty.c:730
 flush_echoes drivers/tty/n_tty.c:791 [inline]
 __receive_buf drivers/tty/n_tty.c:1626 [inline]
 n_tty_receive_buf_common+0x8e4/0xbe0 drivers/tty/n_tty.c:1723
 n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1769
 tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:387
 tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
 receive_buf drivers/tty/tty_buffer.c:445 [inline]
 flush_to_ldisc+0x144/0x360 drivers/tty/tty_buffer.c:495
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3321
 worker_thread+0x582/0x770 kernel/workqueue.c:3402
 kthread+0x489/0x510 kernel/kthread.c:464
 ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffc900011bd280 of 8 bytes by task 31622 on cpu 1:
 process_echoes drivers/tty/n_tty.c:768 [inline]
 n_tty_write+0x161/0xb10 drivers/tty/n_tty.c:2363
 iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
 file_tty_write+0x389/0x670 drivers/tty/tty_io.c:1081
 tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x4a0/0x8e0 fs/read_write.c:686
 ksys_write+0xda/0x1a0 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x40/0x50 fs/read_write.c:746
 x64_sys_call+0x2cdd/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:2
 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

value changed: 0x0000000000000008 -> 0x000000000000000e

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 31622 Comm: syz.8.9036 Tainted: G        W           6.16.0-rc4-syzkaller-00123-g4c06e63b9203 #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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