[moderation] [serial?] KCSAN: data-race in n_tty_flush_buffer / n_tty_lookahead_flow_ctrl (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: bc9ff192a6c9 Merge tag 'net-6.16-rc6' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ab468c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a2f5ccd29a82f8aa
dashboard link: https://syzkaller.appspot.com/bug?extid=c6af600dec0bf367b910
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/cd81278ad98c/disk-bc9ff192.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1fea20ae9800/vmlinux-bc9ff192.xz
kernel image: https://storage.googleapis.com/syzbot-assets/00054e9f79c3/bzImage-bc9ff192.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c6af60...@syzkaller.appspotmail.com

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

write to 0xffffc900017bd270 of 8 bytes by task 16915 on cpu 1:
reset_buffer_flags drivers/tty/n_tty.c:322 [inline]
n_tty_flush_buffer+0xa8/0x180 drivers/tty/n_tty.c:353
tty_ldisc_hangup+0x77/0x370 drivers/tty/tty_ldisc.c:699
__tty_hangup+0x395/0x510 drivers/tty/tty_io.c:621
tty_vhangup drivers/tty/tty_io.c:691 [inline]
tty_ioctl+0x601/0xb80 drivers/tty/tty_io.c:2732
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

read-write to 0xffffc900017bd270 of 8 bytes by task 6273 on cpu 0:
n_tty_lookahead_flow_ctrl+0x48/0x130 drivers/tty/n_tty.c:1491
tty_port_default_lookahead_buf+0x8e/0xc0 drivers/tty/tty_port.c:59
lookahead_bufs drivers/tty/tty_buffer.c:428 [inline]
flush_to_ldisc+0x281/0x360 drivers/tty/tty_buffer.c:498
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0x4cb/0x9d0 kernel/workqueue.c:3321
worker_thread+0x582/0x770 kernel/workqueue.c:3402
kthread+0x489/0x510 kernel/kthread.c:464
ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x0000000000002983 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 6273 Comm: kworker/u8:40 Not tainted 6.16.0-rc5-syzkaller-00121-gbc9ff192a6c9 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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.