KCSAN: data-race in n_tty_receive_buf_common / n_tty_receive_char

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c7d102232649 Merge tag 'net-5.14-rc4' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1557551a300000
kernel config: https://syzkaller.appspot.com/x/.config?x=bf005c115fada019
dashboard link: https://syzkaller.appspot.com/bug?extid=64c4770d211d3132688b
compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+64c477...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_receive_buf_common / n_tty_receive_char

write to 0xffffc90001241018 of 8 bytes by task 22619 on cpu 0:
echo_char_raw drivers/tty/n_tty.c:841 [inline]
eraser drivers/tty/n_tty.c:1076 [inline]
n_tty_receive_char_special drivers/tty/n_tty.c:1308 [inline]
n_tty_receive_buf_standard drivers/tty/n_tty.c:1558 [inline]
__receive_buf drivers/tty/n_tty.c:1577 [inline]
n_tty_receive_buf_common+0x2756/0x4e70 drivers/tty/n_tty.c:1674
n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1703
tiocsti drivers/tty/tty_io.c:2311 [inline]
tty_ioctl+0x968/0x1120 drivers/tty/tty_io.c:2719
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:1069 [inline]
__se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
__x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffc90001241018 of 8 bytes by task 1791 on cpu 1:
add_echo_byte drivers/tty/n_tty.c:840 [inline]
echo_char drivers/tty/n_tty.c:945 [inline]
n_tty_receive_char+0x435/0x6c0 drivers/tty/n_tty.c:1410
n_tty_receive_buf_standard drivers/tty/n_tty.c:1560 [inline]
__receive_buf drivers/tty/n_tty.c:1577 [inline]
n_tty_receive_buf_common+0xf2e/0x4e70 drivers/tty/n_tty.c:1674
n_tty_receive_buf2+0x2e/0x40 drivers/tty/n_tty.c:1709
tty_ldisc_receive_buf+0x5b/0xf0 drivers/tty/tty_buffer.c:471
tty_port_default_receive_buf+0x54/0x80 drivers/tty/tty_port.c:39
receive_buf drivers/tty/tty_buffer.c:491 [inline]
flush_to_ldisc+0x1c5/0x2c0 drivers/tty/tty_buffer.c:543
process_one_work+0x3e9/0x8f0 kernel/workqueue.c:2276
worker_thread+0x636/0xae0 kernel/workqueue.c:2422
kthread+0x262/0x280 kernel/kthread.c:319
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

value changed: 0x00000000000000d6 -> 0x0000000000000124

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1791 Comm: kworker/u4:4 Tainted: G W 5.14.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events_unbound flush_to_ldisc
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.