[moderation] [serial?] KCSAN: data-race in __stop_tty / n_tty_receive_char (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 615d30064886 Merge tag 'trace-v6.8-rc1' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=102179d7e80000
kernel config: https://syzkaller.appspot.com/x/.config?x=e1bd33f45956bbc2
dashboard link: https://syzkaller.appspot.com/bug?extid=0c5cf9e7195331ae3cc3
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/1a66a9307055/disk-615d3006.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c021a1b5a1bd/vmlinux-615d3006.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f7dcf052f898/bzImage-615d3006.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0c5cf9...@syzkaller.appspotmail.com

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

write to 0xffff88813a79d1bc of 1 bytes by task 26390 on cpu 1:
__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:2812
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+0x59/0x120 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff88813a79d1bc of 1 bytes by task 22642 on cpu 0:
n_tty_receive_char+0x3d/0x670 drivers/tty/n_tty.c:1427
n_tty_receive_buf_standard+0x4bd/0x2e20 drivers/tty/n_tty.c:1606
__receive_buf drivers/tty/n_tty.c:1630 [inline]
n_tty_receive_buf_common+0x7e5/0xbc0 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:2633 [inline]
process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2706
worker_thread+0x525/0x730 kernel/workqueue.c:2787
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: 0 PID: 22642 Comm: kworker/u4:8 Not tainted 6.8.0-rc1-syzkaller-00029-g615d30064886 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Workqueue: events_unbound flush_to_ldisc
==================================================================


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