[moderation] [serial?] KCSAN: data-race in n_tty_close / pty_close (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 90b83efa6701 Merge tag 'bpf-next-6.16' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13a7fbf4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c97eebd62683a33d
dashboard link: https://syzkaller.appspot.com/bug?extid=197fd9f24020253ddafd
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
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/93a383fbc67f/disk-90b83efa.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ef537c45c4b6/vmlinux-90b83efa.xz
kernel image: https://storage.googleapis.com/syzbot-assets/871c4dd4722e/bzImage-90b83efa.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+197fd9...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_close / pty_close

write to 0xffff8881198165d5 of 1 bytes by task 4873 on cpu 0:
pty_close+0x126/0x290 drivers/tty/pty.c:61
tty_release+0x1fc/0xb10 drivers/tty/tty_io.c:1754
__fput+0x29b/0x650 fs/file_table.c:465
____fput+0x1c/0x30 fs/file_table.c:493
task_work_run+0x12e/0x1a0 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xe4/0x100 kernel/entry/common.c:114
exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881198165d5 of 1 bytes by task 4874 on cpu 1:
n_tty_packet_mode_flush drivers/tty/n_tty.c:329 [inline]
n_tty_close+0x54/0x120 drivers/tty/n_tty.c:1880
tty_ldisc_close drivers/tty/tty_ldisc.c:455 [inline]
tty_ldisc_kill+0x8a/0x140 drivers/tty/tty_ldisc.c:613
tty_ldisc_hangup+0x2fa/0x370 drivers/tty/tty_ldisc.c:729
__tty_hangup+0x395/0x510 drivers/tty/tty_io.c:624
tty_vhangup drivers/tty/tty_io.c:694 [inline]
tty_ioctl+0x601/0xb80 drivers/tty/tty_io.c:2742
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:893
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:893
x64_sys_call+0x19a8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x01 -> 0x00

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4874 Comm: syz.1.558 Not tainted 6.15.0-syzkaller-07774-g90b83efa6701 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.