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BUG: KCSAN: data-race in __process_echoes / n_tty_write

write to 0xffffc9000f6fb278 of 8 bytes by task 19088 on cpu 1:
 __process_echoes+0x603/0x650 drivers/tty/n_tty.c:751
 flush_echoes drivers/tty/n_tty.c:812 [inline]
 __receive_buf drivers/tty/n_tty.c:1564 [inline]
 n_tty_receive_buf_common+0x4a0b/0x4c40 drivers/tty/n_tty.c:1658
 n_tty_receive_buf2+0x2e/0x40 drivers/tty/n_tty.c:1693
 tty_ldisc_receive_buf+0x5b/0xf0 drivers/tty/tty_buffer.c:452
 paste_selection+0x215/0x300 drivers/tty/vt/selection.c:408
 tioclinux+0xee/0x3e0 drivers/tty/vt/vt.c:3204
 vt_ioctl+0x263/0x13c0 drivers/tty/vt/vt_ioctl.c:762
 tty_ioctl+0x6be/0x970 drivers/tty/tty_io.c:2778
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:856
 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+0x46/0xb0

read to 0xffffc9000f6fb278 of 8 bytes by task 19101 on cpu 0:
 process_echoes drivers/tty/n_tty.c:789 [inline]
 n_tty_write+0x14e/0xb40 drivers/tty/n_tty.c:2283
 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_readv_writev+0x27b/0x300
 do_iter_write+0x16f/0x5c0 fs/read_write.c:868
 vfs_writev fs/read_write.c:941 [inline]
 do_writev+0x256/0x4b0 fs/read_write.c:984
 __do_sys_writev fs/read_write.c:1057 [inline]
 __se_sys_writev fs/read_write.c:1054 [inline]
 __x64_sys_writev+0x41/0x50 fs/read_write.c:1054
 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+0x46/0xb0

value changed: 0x000000000000358f -> 0x0000000000003597

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 19101 Comm: syz-executor.2 Not tainted 5.19.0-rc1-syzkaller-00003-ge71e60cd74df-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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