[moderation] [serial?] KCSAN: data-race in n_tty_flush_buffer / n_tty_poll

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 07d9df80082b Merge tag 'perf-tools-fixes-for-v6.17-2025-08..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10991634580000
kernel config: https://syzkaller.appspot.com/x/.config?x=86a2212b48ce4ce2
dashboard link: https://syzkaller.appspot.com/bug?extid=0425d0c83707555e0188
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
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/4d171f55c84c/disk-07d9df80.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a98c7e116e81/vmlinux-07d9df80.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7681910e0d3d/bzImage-07d9df80.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0425d0...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_flush_buffer / n_tty_poll

write to 0xffffc90006d5b000 of 24 bytes by task 9965 on cpu 0:
reset_buffer_flags drivers/tty/n_tty.c:314 [inline]
n_tty_flush_buffer+0x52/0x180 drivers/tty/n_tty.c:353
tty_ldisc_hangup+0x77/0x370 drivers/tty/tty_ldisc.c:699
__tty_hangup+0x3c2/0x540 drivers/tty/tty_io.c:621
tty_vhangup+0x17/0x20 drivers/tty/tty_io.c:691
pty_close+0x266/0x290 drivers/tty/pty.c:79
tty_release+0x1fc/0xb10 drivers/tty/tty_io.c:1745
__fput+0x298/0x650 fs/file_table.c:468
____fput+0x1c/0x30 fs/file_table.c:496
task_work_run+0x131/0x1a0 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:43
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffc90006d5b008 of 8 bytes by task 9968 on cpu 1:
input_available_p drivers/tty/n_tty.c:1926 [inline]
n_tty_poll+0x2dd/0x450 drivers/tty/n_tty.c:2456
tty_poll+0x79/0xf0 drivers/tty/tty_io.c:2199
vfs_poll include/linux/poll.h:82 [inline]
io_poll_check_events io_uring/poll.c:262 [inline]
io_poll_task_func+0x143/0x910 io_uring/poll.c:317
io_handle_tw_list+0xcc/0x1c0 io_uring/io_uring.c:1102
tctx_task_work_run+0x6d/0x1a0 io_uring/io_uring.c:1167
tctx_task_work+0x3f/0x80 io_uring/io_uring.c:1185
task_work_run+0x131/0x1a0 kernel/task_work.c:227
get_signal+0xe13/0xf70 kernel/signal.c:2807
arch_do_signal_or_restart+0x96/0x480 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x7a/0x100 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x1d6/0x200 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x000000000000892e -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 9968 Comm: syz.1.2591 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================


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[syzbot]

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