[moderation] [serial?] KCSAN: data-race in n_tty_lookahead_flow_ctrl / tty_set_termios (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c85af715cac0 Merge tag 'vboxsf-v6.9-1' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16c58223180000
kernel config: https://syzkaller.appspot.com/x/.config?x=d024e89f7bb376ce
dashboard link: https://syzkaller.appspot.com/bug?extid=caef20e248980f1bf2f5
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/cb8a24fb67ab/disk-c85af715.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/58c43ae1e149/vmlinux-c85af715.xz
kernel image: https://storage.googleapis.com/syzbot-assets/70be5623c16c/bzImage-c85af715.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+caef20...@syzkaller.appspotmail.com

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

read-write to 0xffff88810ea80508 of 4 bytes by task 15253 on cpu 0:
unset_locked_termios drivers/tty/tty_ioctl.c:214 [inline]
tty_set_termios+0xfa/0x8b0 drivers/tty/tty_ioctl.c:340
set_termios+0x365/0x4e0 drivers/tty/tty_ioctl.c:520
tty_mode_ioctl+0x391/0x5d0
n_tty_ioctl_helper+0x8d/0x240 drivers/tty/tty_ioctl.c:986
n_tty_ioctl+0xfd/0x200 drivers/tty/n_tty.c:2511
tty_ioctl+0x886/0xbe0 drivers/tty/tty_io.c:2812
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:904 [inline]
__se_sys_ioctl+0xd3/0x150 fs/ioctl.c:890
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:890
do_syscall_64+0xd3/0x1d0
entry_SYSCALL_64_after_hwframe+0x72/0x7a

read to 0xffff88810ea80508 of 4 bytes by task 3591 on cpu 1:
n_tty_lookahead_flow_ctrl+0x5b/0x130 drivers/tty/n_tty.c:1509
tty_port_default_lookahead_buf+0x8a/0xc0 drivers/tty/tty_port.c:59
lookahead_bufs drivers/tty/tty_buffer.c:428 [inline]
flush_to_ldisc+0x31c/0x410 drivers/tty/tty_buffer.c:498
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0x465/0x990 kernel/workqueue.c:3335
worker_thread+0x526/0x730 kernel/workqueue.c:3416
kthread+0x1d1/0x210 kernel/kthread.c:388
ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

value changed: 0x00000401 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3591 Comm: kworker/u8:8 Tainted: G W 6.9.0-rc2-syzkaller-00080-gc85af715cac0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: events_unbound flush_to_ldisc
==================================================================


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