KCSAN: data-race in __process_echoes / n_tty

KCSAN: data-race in __process_echoes / n_tty_write
Status: auto-closed as invalid on 2020/09/20 17:41
Reported-by: syzbot+@syzkaller.appspotmail.com
First crash: 511d, last: 470d

similar bugs (4):
Kernel	Title	Count	Last	Reported	Patched	Status
upstream	KCSAN: data-race in __process_echoes / n_tty_write (3)	7	183d	248d	0/22	auto-closed as invalid on 2021/07/04 10:36
upstream	KCSAN: data-race in __process_echoes / n_tty_write (4)	1	141d	141d	0/22	auto-closed as invalid on 2021/08/15 21:06
upstream	KCSAN: data-race in __process_echoes / n_tty_write (2)	4	338d	357d	0/22	auto-closed as invalid on 2021/01/30 23:25
upstream	KCSAN: data-race in __process_echoes / n_tty_write (5)	1	61d	61d	0/22	auto-closed as invalid on 2021/11/04 02:47

Sample crash report:

==================================================================
BUG: KCSAN: data-race in __process_echoes / n_tty_write

write to 0xffffc900034df278 of 8 bytes by task 7575 on cpu 1:
 __process_echoes+0x5f7/0x650 drivers/tty/n_tty.c:768
 flush_echoes drivers/tty/n_tty.c:829 [inline]
 __receive_buf drivers/tty/n_tty.c:1648 [inline]
 n_tty_receive_buf_common+0x1bdf/0x1e70 drivers/tty/n_tty.c:1742
 n_tty_receive_buf2+0x2e/0x40 drivers/tty/n_tty.c:1777
 tty_ldisc_receive_buf+0x61/0xf0 drivers/tty/tty_buffer.c:461
 tty_port_default_receive_buf+0x54/0x80 drivers/tty/tty_port.c:38
 receive_buf drivers/tty/tty_buffer.c:481 [inline]
 flush_to_ldisc+0x1b5/0x2b0 drivers/tty/tty_buffer.c:533
 process_one_work+0x3e1/0x9a0 kernel/workqueue.c:2269
 worker_thread+0x665/0xbe0 kernel/workqueue.c:2415
 kthread+0x20d/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffffc900034df278 of 8 bytes by task 23798 on cpu 0:
 process_echoes drivers/tty/n_tty.c:806 [inline]
 n_tty_write+0x151/0xae0 drivers/tty/n_tty.c:2319
 do_tty_write drivers/tty/tty_io.c:962 [inline]
 tty_write+0x3fc/0x5e0 drivers/tty/tty_io.c:1046
 vfs_write+0x1df/0x6f0 fs/read_write.c:576
 ksys_write+0xce/0x180 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write fs/read_write.c:640 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:640
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 23798 Comm: syz-executor.2 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================

Crashes (3):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report
ci2-upstream-kcsan-gce	2020/08/16 17:32	upstream	4b6c093e21d3	5ce13532	.config	log	report
ci2-upstream-kcsan-gce	2020/08/01 13:32	upstream	7dc6fd0f3b84	8df85ed9	.config	log	report
ci2-upstream-kcsan-gce	2020/07/06 05:14	upstream	45a5ac7a5cc3	22f87567	.config	log	report