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BUG: KCSAN: data-race in __process_echoes / n_tty_write

write to 0xffffc90000b37280 of 8 bytes by task 9414 on cpu 0:
 __process_echoes+0x5db/0x620 drivers/tty/n_tty.c:755
 flush_echoes drivers/tty/n_tty.c:816 [inline]
 __receive_buf drivers/tty/n_tty.c:1614 [inline]
 n_tty_receive_buf_common+0x8f9/0xbd0 drivers/tty/n_tty.c:1710
 n_tty_receive_buf+0x2f/0x40 drivers/tty/n_tty.c:1750
 tiocsti+0x168/0x1c0 drivers/tty/tty_io.c:2301
 tty_ioctl+0x415/0xbc0 drivers/tty/tty_io.c:2700
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcf/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffffc90000b37280 of 8 bytes by task 9413 on cpu 1:
 process_echoes drivers/tty/n_tty.c:793 [inline]
 n_tty_write+0x16c/0xa80 drivers/tty/n_tty.c:2352
 do_tty_write drivers/tty/tty_io.c:1027 [inline]
 file_tty_write+0x396/0x680 drivers/tty/tty_io.c:1098
 tty_write+0x28/0x30 drivers/tty/tty_io.c:1119
 call_write_iter include/linux/fs.h:1871 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x4ab/0x7d0 fs/read_write.c:584
 ksys_write+0xeb/0x1a0 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x42/0x50 fs/read_write.c:646
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x0000000000000000 -> 0x0000000000000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9413 Comm: syz-executor.4 Not tainted 6.5.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/03/2023
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