[moderation] [serial?] KCSAN: data-race in n_tty_receive_buf_common / n_tty_write (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c10130c234c8 Merge tag 'io_uring-7.1-20260605' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15d69e7a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f571f22917457cd8
dashboard link: https://syzkaller.appspot.com/bug?extid=673dca7e39e70c351425
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/98e04c4df3ef/disk-c10130c2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/77cee0f896d8/vmlinux-c10130c2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7c2f1eb0dbea/bzImage-c10130c2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+673dca...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in n_tty_receive_buf_common / n_tty_write

write to 0xffffc90001a9b020 of 8 bytes by task 25151 on cpu 0:
process_echoes drivers/tty/n_tty.c:766 [inline]
n_tty_write+0x1e4/0xb80 drivers/tty/n_tty.c:2352
iterate_tty_write drivers/tty/tty_io.c:1006 [inline]
file_tty_write+0x378/0x680 drivers/tty/tty_io.c:1081
tty_write+0x25/0x30 drivers/tty/tty_io.c:1102
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x5a6/0x9f0 fs/read_write.c:688
ksys_write+0xdc/0x1a0 fs/read_write.c:740
__do_sys_write fs/read_write.c:751 [inline]
__se_sys_write fs/read_write.c:748 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:748
x64_sys_call+0x27e1/0x3020 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffffc90001a9b020 of 8 bytes by task 13004 on cpu 1:
flush_echoes drivers/tty/n_tty.c:780 [inline]
__receive_buf drivers/tty/n_tty.c:1618 [inline]
n_tty_receive_buf_common+0x869/0xc00 drivers/tty/n_tty.c:1715
n_tty_receive_buf2+0x33/0x40 drivers/tty/n_tty.c:1759
tty_ldisc_receive_buf+0x66/0xf0 drivers/tty/tty_buffer.c:394
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:452 [inline]
flush_to_ldisc+0x148/0x340 drivers/tty/tty_buffer.c:502
process_one_work kernel/workqueue.c:3314 [inline]
process_scheduled_works+0x4f0/0x9c0 kernel/workqueue.c:3397
worker_thread+0x58a/0x780 kernel/workqueue.c:3478
kthread+0x22a/0x280 kernel/kthread.c:436
ret_from_fork+0x146/0x330 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

value changed: 0x0000000000000000 -> 0x0000000000000011

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 13004 Comm: kworker/u8:17 Tainted: G W syzkaller #0 PREEMPT(lazy)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events_unbound flush_to_ldisc
==================================================================


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