[moderation] [serial?] KCSAN: data-race in isig / n_tty_poll

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c8ebd433459b Merge tag 'nfsd-6.19-2' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1383a422580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=a6f6fec32bf08a0b9f6f
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/d4c0e188b92f/disk-c8ebd433.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/25522cdc5fa6/vmlinux-c8ebd433.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a1499d747012/bzImage-c8ebd433.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a6f6fe...@syzkaller.appspotmail.com

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

write to 0xffffc900001da260 of 16 bytes by task 41 on cpu 0:
reset_buffer_flags drivers/tty/n_tty.c:316 [inline]
isig+0x181/0x2f0 drivers/tty/n_tty.c:1092
n_tty_receive_signal_char+0x22/0x460 drivers/tty/n_tty.c:1184
n_tty_receive_char_special drivers/tty/n_tty.c:-1 [inline]
n_tty_receive_buf_standard+0x82f/0x2fe0 drivers/tty/n_tty.c:1580
__receive_buf drivers/tty/n_tty.c:1609 [inline]
n_tty_receive_buf_common+0x7a4/0xc10 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:387
tty_port_default_receive_buf+0x59/0x90 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:445 [inline]
flush_to_ldisc+0x148/0x340 drivers/tty/tty_buffer.c:495
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
worker_thread+0x582/0x770 kernel/workqueue.c:3421
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffffc900001da260 of 8 bytes by task 9389 on cpu 1:
input_available_p drivers/tty/n_tty.c:1913 [inline]
n_tty_poll+0x164/0x450 drivers/tty/n_tty.c:2440
tty_poll+0x79/0xf0 drivers/tty/tty_io.c:2199
vfs_poll include/linux/poll.h:82 [inline]
do_pollfd fs/select.c:866 [inline]
do_poll fs/select.c:909 [inline]
do_sys_poll+0x65e/0xbd0 fs/select.c:1005
__do_sys_ppoll fs/select.c:1111 [inline]
__se_sys_ppoll+0x1b9/0x200 fs/select.c:1091
__x64_sys_ppoll+0x67/0x80 fs/select.c:1091
x64_sys_call+0x22fe/0x3000 arch/x86/include/generated/asm/syscalls_64.h:272
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000000000ad -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 9389 Comm: syz.4.1998 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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