KCSAN: data-race in n_tty_receive_char_special / n_tty_receive_char_special (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 85a2c56c Merge tag 'pm-5.10-rc6' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1200e6b5500000
kernel config: https://syzkaller.appspot.com/x/.config?x=9b9b19d1bde60f8d
dashboard link: https://syzkaller.appspot.com/bug?extid=c8b476f28b4240b598d0
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
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+c8b476...@syzkaller.appspotmail.com

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

read to 0xffffc900056c5018 of 8 bytes by task 8136 on cpu 1:
add_echo_byte drivers/tty/n_tty.c:843 [inline]
echo_char_raw drivers/tty/n_tty.c:923 [inline]
n_tty_receive_char_special+0x20a0/0x3860 drivers/tty/n_tty.c:1347
n_tty_receive_buf_fast drivers/tty/n_tty.c:1610 [inline]
__receive_buf drivers/tty/n_tty.c:1644 [inline]
n_tty_receive_buf_common+0xe2b/0x1df0 drivers/tty/n_tty.c:1742
n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1771
tiocsti drivers/tty/tty_io.c:2198 [inline]
tty_ioctl+0x8e4/0xfd0 drivers/tty/tty_io.c:2572
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
__x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read-write to 0xffffc900056c5018 of 8 bytes by task 15571 on cpu 0:
add_echo_byte drivers/tty/n_tty.c:845 [inline]
echo_char_raw drivers/tty/n_tty.c:923 [inline]
n_tty_receive_char_special+0x20ce/0x3860 drivers/tty/n_tty.c:1347
n_tty_receive_buf_fast drivers/tty/n_tty.c:1610 [inline]
__receive_buf drivers/tty/n_tty.c:1644 [inline]
n_tty_receive_buf_common+0xe2b/0x1df0 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
paste_selection+0x226/0x300 drivers/tty/vt/selection.c:408
tioclinux+0xe5/0x450 drivers/tty/vt/vt.c:3164
vt_ioctl+0xde0/0x20e0 drivers/tty/vt/vt_ioctl.c:823
tty_ioctl+0x9f0/0xfd0 drivers/tty/tty_io.c:2656
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
__x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
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: 15571 Comm: syz-executor.4 Not tainted 5.10.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

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