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SubjectRe: AS spin lock bugs


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.


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