Re: AS spin lock bugs

[Nick Piggin]

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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