[moderation] [serial?] KCSAN: data-race in n_tty_flush_buffer / n_tty_lookahead_flow_ctrl (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 005f6f34bd47 Merge tag 'i2c-for-6.8-rc8' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1290a08e180000
kernel config: https://syzkaller.appspot.com/x/.config?x=68a9b6ec15207f27
dashboard link: https://syzkaller.appspot.com/bug?extid=333a571d385057a2f869
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/4435bc3c55d3/disk-005f6f34.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9cf2cb6508ff/vmlinux-005f6f34.xz
kernel image: https://storage.googleapis.com/syzbot-assets/78e5e0f57bbd/bzImage-005f6f34.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+333a57...@syzkaller.appspotmail.com

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

write to 0xffffc9000129b270 of 8 bytes by task 26929 on cpu 0:
reset_buffer_flags drivers/tty/n_tty.c:328 [inline]
n_tty_flush_buffer+0x9f/0x180 drivers/tty/n_tty.c:359
tty_ldisc_hangup+0x6e/0x360 drivers/tty/tty_ldisc.c:693
__tty_hangup+0x3c6/0x530 drivers/tty/tty_io.c:630
tty_vhangup+0x17/0x20 drivers/tty/tty_io.c:700
pty_close+0x262/0x280 drivers/tty/pty.c:79
tty_release+0x204/0x930 drivers/tty/tty_io.c:1760
__fput+0x299/0x630 fs/file_table.c:376
____fput+0x15/0x20 fs/file_table.c:404
task_work_run+0x135/0x1a0 kernel/task_work.c:180
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0x604/0x16d0 kernel/exit.c:871
do_group_exit+0x101/0x150 kernel/exit.c:1020
get_signal+0xf4e/0x10a0 kernel/signal.c:2893
arch_do_signal_or_restart+0x95/0x4b0 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop kernel/entry/common.c:105 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:201 [inline]
syscall_exit_to_user_mode+0x58/0x120 kernel/entry/common.c:212
do_syscall_64+0xda/0x1d0 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x63/0x6b

read-write to 0xffffc9000129b270 of 8 bytes by task 26927 on cpu 1:
n_tty_lookahead_flow_ctrl+0x48/0x130 drivers/tty/n_tty.c:1507
tty_port_default_lookahead_buf+0x87/0xb0 drivers/tty/tty_port.c:59
lookahead_bufs drivers/tty/tty_buffer.c:427 [inline]
flush_to_ldisc+0x30c/0x400 drivers/tty/tty_buffer.c:497
process_one_work kernel/workqueue.c:2633 [inline]
process_scheduled_works+0x5b8/0xa40 kernel/workqueue.c:2706
worker_thread+0x525/0x730 kernel/workqueue.c:2787
kthread+0x1d7/0x210 kernel/kthread.c:388
ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:243

value changed: 0x000000000000052c -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 26927 Comm: kworker/u4:74 Not tainted 6.8.0-rc7-syzkaller-00238-g005f6f34bd47 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
Workqueue: events_unbound flush_to_ldisc
==================================================================


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