[moderation] [serial?] KCSAN: data-race in __stop_tty / pty_write (15)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 499551201b5f Merge tag 'arm64-fixes' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1658b2df980000
kernel config: https://syzkaller.appspot.com/x/.config?x=67aa69407438e9cf
dashboard link: https://syzkaller.appspot.com/bug?extid=fd81d1588c86610e24e8
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/c483c0e0089f/disk-49955120.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/92a93ab3fbb1/vmlinux-49955120.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8ffbe49023f4/bzImage-49955120.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fd81d1...@syzkaller.appspotmail.com

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

write to 0xffff888135a565bc of 1 bytes by task 22414 on cpu 0:
__stop_tty+0x42/0x90 drivers/tty/tty_io.c:747
n_tty_ioctl_helper+0x223/0x240 drivers/tty/tty_ioctl.c:955
n_tty_ioctl+0xfd/0x200 drivers/tty/n_tty.c:2521
tty_ioctl+0x87a/0xbe0 drivers/tty/tty_io.c:2812
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0xc9/0x140 fs/ioctl.c:892
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
x64_sys_call+0x1690/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888135a565bc of 1 bytes by task 10763 on cpu 1:
pty_write+0x26/0xa0 drivers/tty/pty.c:115
tty_put_char+0x8d/0xc0 drivers/tty/tty_io.c:3168
__process_echoes+0x12c/0x6b0 drivers/tty/n_tty.c:724
flush_echoes drivers/tty/n_tty.c:807 [inline]
__receive_buf drivers/tty/n_tty.c:1642 [inline]
n_tty_receive_buf_common+0x8f9/0xbe0 drivers/tty/n_tty.c:1739
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1785
tty_ldisc_receive_buf+0x63/0x100 drivers/tty/tty_buffer.c:387
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:445 [inline]
flush_to_ldisc+0x1ce/0x410 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3229 [inline]
process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3310
worker_thread+0x51d/0x6f0 kernel/workqueue.c:3391
kthread+0x1d1/0x210 kernel/kthread.c:389
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 10763 Comm: kworker/u8:30 Not tainted 6.13.0-rc3-syzkaller-00209-g499551201b5f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
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.