[moderation] [serial?] KCSAN: data-race in __stop_tty / pty_write (12)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 88035e5694a8 Merge tag 'hid-for-linus-2023121201' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=116e362ae80000
kernel config: https://syzkaller.appspot.com/x/.config?x=d6f4b50a94fc12a6
dashboard link: https://syzkaller.appspot.com/bug?extid=75bffff65389d96c5264
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bcfa87ceea25/disk-88035e56.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5e39c99719af/vmlinux-88035e56.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b47f2fa75492/bzImage-88035e56.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+75bfff...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __stop_tty / pty_write

write to 0xffff88813c322dbc of 1 bytes by task 14431 on cpu 0:
__stop_tty+0x42/0x90 drivers/tty/tty_io.c:753
n_tty_ioctl_helper+0x21f/0x240 drivers/tty/tty_ioctl.c:955
n_tty_ioctl+0xfd/0x200 drivers/tty/n_tty.c:2511
tty_ioctl+0x875/0xbc0 drivers/tty/tty_io.c:2789
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:871 [inline]
__se_sys_ioctl+0xcf/0x140 fs/ioctl.c:857
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:857
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0x44/0x110 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff88813c322dbc of 1 bytes by task 3471 on cpu 1:
pty_write+0x26/0xa0 drivers/tty/pty.c:115
tty_put_char+0x83/0xb0 drivers/tty/tty_io.c:3145
n_tty_process_echo_ops drivers/tty/n_tty.c:663 [inline]
__process_echoes+0x393/0x6a0 drivers/tty/n_tty.c:709
flush_echoes drivers/tty/n_tty.c:807 [inline]
__receive_buf drivers/tty/n_tty.c:1632 [inline]
n_tty_receive_buf_common+0x8e6/0xbc0 drivers/tty/n_tty.c:1729
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1775
tty_ldisc_receive_buf+0x60/0xe0 drivers/tty/tty_buffer.c:386
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x1ca/0x400 drivers/tty/tty_buffer.c:494
process_one_work kernel/workqueue.c:2627 [inline]
process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2700
worker_thread+0x525/0x730 kernel/workqueue.c:2781
kthread+0x1d7/0x210 kernel/kthread.c:388
ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3471 Comm: kworker/u4:8 Not tainted 6.7.0-rc5-syzkaller-00042-g88035e5694a8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
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.