KCSAN: data-race in n_tty_receive_char / n_tty_receive_char

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7d2a07b76933 Linux 5.14
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13898691300000
kernel config: https://syzkaller.appspot.com/x/.config?x=798993b37cff5f3b
dashboard link: https://syzkaller.appspot.com/bug?extid=79da004c606ae02b8613
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+79da00...@syzkaller.appspotmail.com

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

write to 0xffffc90000de1000 of 8 bytes by task 22934 on cpu 1:
put_tty_queue drivers/tty/n_tty.c:316 [inline]
n_tty_receive_char+0x622/0x6c0 drivers/tty/n_tty.c:1416
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_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 0xffffc90000de1000 of 8 bytes by task 26313 on cpu 0:
put_tty_queue drivers/tty/n_tty.c:315 [inline]
n_tty_receive_char+0x5fc/0x6c0 drivers/tty/n_tty.c:1416
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
paste_selection+0x215/0x300 drivers/tty/vt/selection.c:408
tioclinux+0xe5/0x450 drivers/tty/vt/vt.c:3164
vt_ioctl+0x26e/0x2060 drivers/tty/vt/vt_ioctl.c:760
tty_ioctl+0xa24/0x1120 drivers/tty/tty_io.c:2805
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

value changed: 0x00000000000005fd -> 0x00000000000005fe

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 26313 Comm: syz-executor.3 Tainted: G W 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

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