linux-kernel - Re: [PATCH 2/6] kernel: add task

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Date:   Thu, 8 Oct 2020 07:38:05 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     linux-kernel@...r.kernel.org, io-uring@...r.kernel.org,
        peterz@...radead.org, tglx@...utronix.de
Subject: Re: [PATCH 2/6] kernel: add task_sigpending() helper

On 10/8/20 7:24 AM, Oleg Nesterov wrote:
> On 10/05, Jens Axboe wrote:
>>
>> @@ -4447,7 +4447,7 @@ SYSCALL_DEFINE0(pause)
>>  		__set_current_state(TASK_INTERRUPTIBLE);
>>  		schedule();
>>  	}
>> -	return -ERESTARTNOHAND;
>> +	return task_sigpending(current) ? -ERESTARTNOHAND : -ERESTARTSYS;
>>  }
>>
>>  #endif
>> @@ -4462,7 +4462,7 @@ static int sigsuspend(sigset_t *set)
>>  		schedule();
>>  	}
>>  	set_restore_sigmask();
>> -	return -ERESTARTNOHAND;
>> +	return task_sigpending(current) ? -ERESTARTNOHAND : -ERESTARTSYS;
>>  }
> 
> Both changes are equally wrong. Why do you think sigsuspend() should ever
> return -ERESTARTSYS ?
> 
> If get_signal() deques a signal, handle_signal() will restart this syscall
> if ERESTARTSYS, this is wrong.

The intent was that if we get woken up and signal_pending() is true, then
we want to restart it if we're just doing TIF_SIGNAL_NOTIFY. But I guess
it can't be 100% reliable, even if TIF_SIGPENDING isn't set at this point,
but it is by the time a signal is attempted dequeued.

I'll drop these too, thanks Oleg.

-- 
Jens Axboe