On 10/12/2015 01:58 PM, Peter Zijlstra wrote:
> On Mon, Oct 12, 2015 at 12:03:06PM +0200, Daniel Wagner wrote:
>> On 10/12/2015 11:17 AM, Daniel Wagner wrote:
>>> On 09/09/2015 04:26 PM, Peter Zijlstra wrote:
>>>> On Wed, Sep 09, 2015 at 02:05:29PM +0200, Daniel Wagner wrote:
>>>>> @@ -50,10 +50,10 @@ void complete_all(struct completion *x)
>>>>> {
>>>>> unsigned long flags;
>>>>>
>>>>> - spin_lock_irqsave(&x->wait.lock, flags);
>>>>> + raw_spin_lock_irqsave(&x->wait.lock, flags);
>>>>> x->done += UINT_MAX/2;
>>>>> - __wake_up_locked(&x->wait, TASK_NORMAL, 0);
>>>>> - spin_unlock_irqrestore(&x->wait.lock, flags);
>>>>> + swake_up_locked(&x->wait);
>>>>> + raw_spin_unlock_irqrestore(&x->wait.lock, flags);
>>>>> }
>>>>> EXPORT_SYMBOL(complete_all);
>>>>
>>>> I don't think that's correct; __wake_up_locked(.nr=0) would wake all
>>>> waiters, where swake_up_locked() will only wake one.
>>>
>>> I read that x->done should be protected via wait.lock during the whole
>>> operation. swake_up_all() will release and reacquire the lock while
>>> processing the all waiters. So we need to get
>>>
>>> Could we play a trick like setting the highest bit in done for
>>> indicating the complete_all() operation. The UINT_MAX/2 update looks
>>> like do this by setting a value which has the biggest offset from 0 (but
>>> why adding instead of just going for assigning...).
>>
>>
>> I had something like this here in mind:
>
> I'm not exactly sure what problem you're trying to solve here.. The fact
> that we cannot call swake_all() while holding &x->wait.lock, or the fact
> that complete_all() is typically called from a context which cannot do
> swake_all() either?
The first one.
> Note:
>
> Documentation/scheduler/completion.txt:complete() and complete_all() can be
> called in hard-irq/atomic context safely.
>
> Which is very much _NOT_ true of swake_all().
Heh and I thought I got this right.
Looks like completion.c cannot use swait here. Or do you have an idea
how to do it? I was thinking on deferring the wake all call from
hard-irq/atomic but I guess this something to avoided.
cheers,
daniel
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
