[moderation] [serial?] KCSAN: data-race in __stop_tty / pty_write_room (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 10d48d70e82d Merge tag 'char-misc-6.8-rc8' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=128d78ae180000
kernel config: https://syzkaller.appspot.com/x/.config?x=68a9b6ec15207f27
dashboard link: https://syzkaller.appspot.com/bug?extid=0577961eb1eae3e7066e
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/63c2b855c8c2/disk-10d48d70.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1ecb62ac7a94/vmlinux-10d48d70.xz
kernel image: https://storage.googleapis.com/syzbot-assets/58fba816c8de/bzImage-10d48d70.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+057796...@syzkaller.appspotmail.com

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

write to 0xffff88812016c9bc of 1 bytes by task 22195 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: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+0xcd/0x1d0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff88812016c9bc of 1 bytes by task 1522 on cpu 1:
pty_write_room+0x1c/0x70 drivers/tty/pty.c:131
tty_write_room+0x38/0x50 drivers/tty/tty_ioctl.c:69
__process_echoes+0x36/0x6a0 drivers/tty/n_tty.c:703
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:2633 [inline]
process_scheduled_works+0x5b8/0xa40 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:243

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1522 Comm: kworker/u4:5 Not tainted 6.8.0-rc7-syzkaller-00229-g10d48d70e82d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
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.