[moderation] [serial?] KCSAN: data-race in do_con_write / stop_tty (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 128c8f96eb86 Merge tag 'drm-fixes-2025-02-14' of https://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14506098580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c8889d5a0d6060f3
dashboard link: https://syzkaller.appspot.com/bug?extid=39a480dd00bdafa10444
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/bbf7e527966e/disk-128c8f96.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7b968fc47406/vmlinux-128c8f96.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1b3ab90aa562/bzImage-128c8f96.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+39a480...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_con_write / stop_tty

write to 0xffff8881171471bc of 1 bytes by task 10340 on cpu 1:
__stop_tty drivers/tty/tty_io.c:747 [inline]
stop_tty+0x58/0xc0 drivers/tty/tty_io.c:771
n_tty_receive_char_flow_ctrl+0x87/0x1a0 drivers/tty/n_tty.c:1254
n_tty_receive_char_special drivers/tty/n_tty.c:1359 [inline]
n_tty_receive_buf_standard+0x4e1/0x2e30 drivers/tty/n_tty.c:1604
__receive_buf drivers/tty/n_tty.c:1640 [inline]
n_tty_receive_buf_common+0x830/0xbd0 drivers/tty/n_tty.c:1739
n_tty_receive_buf+0x30/0x40 drivers/tty/n_tty.c:1779
tiocsti+0x166/0x1d0 drivers/tty/tty_io.c:2299
tty_ioctl+0x409/0xbe0 drivers/tty/tty_io.c:2716
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:906 [inline]
__se_sys_ioctl+0xc9/0x140 fs/ioctl.c:892
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:892
x64_sys_call+0x1690/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881171471bc of 1 bytes by task 10338 on cpu 0:
do_con_write+0x1a29/0x25f0 drivers/tty/vt/vt.c:3072
con_write+0x26/0x40 drivers/tty/vt/vt.c:3432
process_output_block drivers/tty/n_tty.c:574 [inline]
n_tty_write+0x843/0xb80 drivers/tty/n_tty.c:2389
iterate_tty_write drivers/tty/tty_io.c:1015 [inline]
file_tty_write+0x37a/0x680 drivers/tty/tty_io.c:1090
tty_write+0x28/0x30 drivers/tty/tty_io.c:1111
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0x77b/0x920 fs/read_write.c:679
ksys_write+0xe8/0x1b0 fs/read_write.c:731
__do_sys_write fs/read_write.c:742 [inline]
__se_sys_write fs/read_write.c:739 [inline]
__x64_sys_write+0x42/0x50 fs/read_write.c:739
x64_sys_call+0x287e/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 10338 Comm: syz.7.2500 Tainted: G W 6.14.0-rc2-syzkaller-00185-g128c8f96eb86 #0
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
==================================================================


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[syzbot]

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