[moderation] [serial?] KCSAN: data-race in n_tty_poll / tty_set_termios (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7df48e363130 Merge tag 'for-linus' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16a45cba580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3a78dd265deac3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=9e777dfa1bd5e087c7c8
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/5d6b152559f3/disk-7df48e36.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d67317037637/vmlinux-7df48e36.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d000756d577f/bzImage-7df48e36.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9e777d...@syzkaller.appspotmail.com

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

write to 0xffff8881194b2908 of 44 bytes by task 11799 on cpu 1:
tty_set_termios+0xc0/0x910 drivers/tty/tty_ioctl.c:335
set_termios+0x4a7/0x4f0 drivers/tty/tty_ioctl.c:512
tty_mode_ioctl+0x37f/0x5b0 drivers/tty/tty_ioctl.c:-1
n_tty_ioctl_helper+0x87/0x370 drivers/tty/tty_ioctl.c:982
n_tty_ioctl+0x101/0x230 drivers/tty/n_tty.c:2496
tty_ioctl+0x83e/0xb80 drivers/tty/tty_io.c:2801
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x1563/0x3020 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881194b2914 of 4 bytes by task 11796 on cpu 0:
input_available_p drivers/tty/n_tty.c:1912 [inline]
n_tty_poll+0x12e/0x450 drivers/tty/n_tty.c:2440
tty_poll+0x79/0xf0 drivers/tty/tty_io.c:2199
vfs_poll include/linux/poll.h:82 [inline]
__io_arm_poll_handler+0x1ec/0xc30 io_uring/poll.c:586
io_arm_apoll+0x2eb/0x430 io_uring/poll.c:694
io_arm_poll_handler+0x12f/0x160 io_uring/poll.c:723
io_queue_async+0x25d/0x320 io_uring/io_uring.c:1615
io_queue_sqe io_uring/io_uring.c:1641 [inline]
io_submit_sqe io_uring/io_uring.c:1920 [inline]
io_submit_sqes+0xbe2/0x1230 io_uring/io_uring.c:2043
__do_sys_io_uring_enter io_uring/io_uring.c:2604 [inline]
__se_sys_io_uring_enter+0x1c9/0xf50 io_uring/io_uring.c:2539
__x64_sys_io_uring_enter+0x78/0x90 io_uring/io_uring.c:2539
x64_sys_call+0x1e16/0x3020 arch/x86/include/generated/asm/syscalls_64.h:427
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00008a3b -> 0x00000008

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 11796 Comm: syz.8.1039 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


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