Re: AS spin lock bugs

[Nick Piggin <piggin@cyberone.com.au>]

Jens Axboe wrote:

>On Thu, Nov 13 2003, Jens Axboe wrote:
>
>>On Thu, Nov 13 2003, Nick Piggin wrote:
>>
>>>
>>>Jens Axboe wrote:
>>>
>>>
>>>>On Thu, Nov 13 2003, Jens Axboe wrote:
>>>>
>>>>
>>>>>@@ -959,12 +960,12 @@
>>>>>	if (!aic)
>>>>>		return;
>>>>>
>>>>>-	spin_lock(&aic->lock);
>>>>>+	spin_lock_irqsave(&aic->lock, flags);
>>>>>	if (arq->is_sync == REQ_SYNC) {
>>>>>		set_bit(AS_TASK_IORUNNING, &aic->state);
>>>>>		aic->last_end_request = jiffies;
>>>>>	}
>>>>>-	spin_unlock(&aic->lock);
>>>>>+	spin_unlock_irqrestore(&aic->lock, flags);
>>>>>
>>>>>	put_io_context(arq->io_context);
>>>>>}
>>>>>
>>>>>
>>>>BTW, this looks bogus. Why do you need any locking there?
>>>>
>>>>
>>>To prevent a request completion on another queue on another CPU from
>>>racing with request insertion: last_end_request is undefined if the
>>>flag is not set. I guess you could flip the statements and put a
>>>smp_mb between them. Probably not worth the trouble though.
>>>
>>No better to make it explicit, probably doesn't matter much in
>>real-life. Thanks for the clarifications.
>>
>
>Ah, it would be clearer as:
>
>	if (arq->is_sync == REQ_SYNC) {
>		spin_lock(&aic->lock);
>		set_bit(AS_TASK_IORUNNING, &aic->state);
>		aic->last_end_request = jiffies;
>		spin_unlock(&aic->lock);
>	}
>
>Then it doesn't need comments :)
>

Yeah thats was a bit silly of me I see why you got confused. I
have actually fixed this up in mm3. So it should get through to
Linus sometime after 2.6.0.