KCSAN: data-race in __process_echoes / n_tty_receive_char_special (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fb0155a0 Merge tag 'nfs-for-5.9-3' of git://git.linux-nfs...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16a378f3900000
kernel config: https://syzkaller.appspot.com/x/.config?x=d3bb4312bebb1dd3
dashboard link: https://syzkaller.appspot.com/bug?extid=eeb41c1ab2d66c4e3057
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
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+eeb41c...@syzkaller.appspotmail.com

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

write to 0xffffc900069e7120 of 1 bytes by task 25259 on cpu 1:
add_echo_byte drivers/tty/n_tty.c:843 [inline]
echo_char drivers/tty/n_tty.c:948 [inline]
n_tty_receive_char_special+0x3246/0x3a70 drivers/tty/n_tty.c:1339
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+0xe48/0x1e70 drivers/tty/n_tty.c:1742
n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1771
tiocsti drivers/tty/tty_io.c:2196 [inline]
tty_ioctl+0x8e3/0xfd0 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 to 0xffffc900069e7120 of 1 bytes by task 10407 on cpu 0:
echo_buf drivers/tty/n_tty.c:149 [inline]
__process_echoes+0x564/0x650 drivers/tty/n_tty.c:759
commit_echoes drivers/tty/n_tty.c:794 [inline]
n_tty_receive_char_fast drivers/tty/n_tty.c:1449 [inline]
n_tty_receive_buf_fast drivers/tty/n_tty.c:1609 [inline]
__receive_buf drivers/tty/n_tty.c:1644 [inline]
n_tty_receive_buf_common+0x14f3/0x1e70 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10407 Comm: kworker/u4:5 Not tainted 5.9.0-rc7-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.