Re: [PATCH 1/2] bcache: ignore pending signals in bcache_device_init()

Coly Li
2020-03-02T17:16:59Z

On 2020/3/2 9:49 下午, Oleg Nesterov wrote:
> On 03/02, Michal Hocko wrote:
>>
>> I cannot really comment on the bcache part because I am not familiar
>> with the code.
>
> same here...
>
>>> This patch calls flush_signals() in bcache_device_init() if there is
>>> pending signal for current process. It avoids bcache registration
>>> failure in system boot up time due to bcache udev rule timeout.
>>
>> this sounds like a wrong way to address the issue. Killing the udev
>> worker is a userspace policy and the kernel shouldn't simply ignore it.
>
> Agreed. If nothing else, if a userspace process has pending SIKILL then
> flush_signals() is very wrong.
>
>> Btw. Oleg, I have noticed quite a lot of flush_signals usage in the
>> drivers land and I have really hard time to understand their purpose.
>
> Heh. I bet most if not all users of flush_signals() are simply wrong.
>
>> What is the actual valid usage of this function?
>
> I thinks it should die... It was used by kthreads, but today
> signal_pending() == T is only possible if kthread does allow_signal(),
> and in this case it should probably use kernel_dequeue_signal().
>
>
> Say, io_sq_thread(). Why does it do
>
> if (signal_pending(current))
> flush_signals(current);
>
> afaics this kthread doesn't use allow_signal/allow_kernel_signal, this
> means that signal_pending() must be impossible even if this kthread sleeps
> in TASK_INTERRUPTIBLE state. Add Jens.

Hi Oleg,

Can I use disallow_signal() before the registration begins and use
allow_signal() after the registration done. Is this a proper way to
ignore the signal sent by udevd for timeout ?

For me the above method seems to solve my problem too.

Thanks.

--

Coly Li