Re: AS spin lock bugs

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

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.