On 2020/3/3 1:19 上午, Jens Axboe wrote: > On 3/2/20 10:16 AM, Coly Li wrote: >> 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. > > Really seems to me like you're going about this all wrong. The issue is > that systemd is killing the startup, because it's taking too long. Don't > try and work around that, ensure the timeout is appropriate. > Copied. Then let me try how to make event_timeout works on my udevd. If it works without other side effect, I will revert existing flush_signals() patches. > What if someone else tried to kill the startup? It'd be pretty > frustrating that it was impossible, just because signals were blocked or > flushed. The assumption that systemd is the ONLY task that would want to > kill it is flawed. > Indeed now the bcache registration can not be killed. I guess it is because the mutex lock held during the metadata checking. Sure I will look at how to extend udevd timeout value now, and ask for help later. Thanks. -- Coly Li
