[moderation] [serial?] KCSAN: data-race in n_tty_flush_buffer / n_tty_poll (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 603c05a1639f Merge tag 'nfs-for-6.19-2' of git://git.linux..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1757adfa580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c160236e1ef1e401
dashboard link: https://syzkaller.appspot.com/bug?extid=4530758e86e7cf7b73ae
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/04a4e867f4c0/disk-603c05a1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4ad8770d21bd/vmlinux-603c05a1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6cd2ba5db9c7/bzImage-603c05a1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+453075...@syzkaller.appspotmail.com

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

read to 0xffffc900021c5260 of 8 bytes by task 24188 on cpu 0:
input_available_p drivers/tty/n_tty.c:1913 [inline]
n_tty_poll+0x2a8/0x450 drivers/tty/n_tty.c:2444
tty_poll+0x79/0xf0 drivers/tty/tty_io.c:2199
vfs_poll include/linux/poll.h:82 [inline]
select_poll_one fs/select.c:480 [inline]
do_select+0x8f1/0xf40 fs/select.c:536
core_sys_select+0x3dc/0x6e0 fs/select.c:677
do_pselect fs/select.c:759 [inline]
__do_sys_pselect6 fs/select.c:798 [inline]
__se_sys_pselect6+0x213/0x280 fs/select.c:789
__x64_sys_pselect6+0x78/0x90 fs/select.c:789
x64_sys_call+0x2e98/0x3000 arch/x86/include/generated/asm/syscalls_64.h:271
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffffc900021c5260 of 16 bytes by task 24187 on cpu 1:
reset_buffer_flags drivers/tty/n_tty.c:316 [inline]
n_tty_flush_buffer+0x61/0x1d0 drivers/tty/n_tty.c:350
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+0x2c5/0x2f0 drivers/tty/pty.c:77
tty_release+0x1ff/0xb10 drivers/tty/tty_io.c:1745
__fput+0x29b/0x650 fs/file_table.c:468
____fput+0x1c/0x30 fs/file_table.c:496
task_work_run+0x131/0x1a0 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:44 [inline]
exit_to_user_mode_loop+0x1fe/0x740 kernel/entry/common.c:75
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
do_syscall_64+0x1dd/0x2b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 24187 Comm: syz.2.21631 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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