Re: [Stable-review] [93/93] dm mpath: fix stall when requeueing io

[Linus Torvalds]

On Tue, 23 Feb 2010, Greg KH wrote:
> On Sun, Feb 21, 2010 at 05:07:25PM +0100, Stefan Bader wrote:
> > > 
> > > Signed-off-by: Kiyoshi Ueda <k-ueda@xxxxxxxxxxxxx>
> > > Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
> > > Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
> > >
> > >  		blk_start_request(rq);
> > >  		spin_unlock(q->queue_lock);
> > > -		map_request(ti, rq, md);
> > > +		if (map_request(ti, rq, md))
> > > +			goto requeued;
> > >  		spin_lock_irq(q->queue_lock);
> > >  	}
> > 
> > While looking over the code I also noticed that the spinlock is dropped with
> > spin_unlock and then reacquired with spin_lock_irq. Isn't the irq version too
> > much in that case? Or was the intention to have interrupts enabled when unlocking?
> 
> Ick, thanks for the review.  I'll drop this patch for now and fix it up
> in the next release if needed.

This part of the commentary seems to be relevant for mainline too. 

According to git logs, this spin_unlock/spin_lock_irq imbalance goes back 
to commit cec47e3d4a (last June). Maybe there's some reason for it, but it 
does look odd.

Ueda-san, Nomura-san, Alasdair? Comments?

			Linus
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