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

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Date:	Tue, 23 Feb 2010 09:00:58 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Greg KH <greg@...ah.com>
cc:	Stefan Bader <stefan.bader@...onical.com>,
	Greg KH <gregkh@...e.de>, Kiyoshi Ueda <k-ueda@...jp.nec.com>,
	linux-kernel@...r.kernel.org, stable-review@...nel.org,
	alan@...rguk.ukuu.org.uk, Junichi Nomura <j-nomura@...jp.nec.com>,
	akpm@...ux-foundation.org, stable@...nel.org,
	Alasdair G Kergon <agk@...hat.com>
Subject: Re: [Stable-review] [93/93] dm mpath: fix stall when requeueing io



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@...jp.nec.com>
> > > Signed-off-by: Jun'ichi Nomura <j-nomura@...jp.nec.com>
> > > Signed-off-by: Alasdair G Kergon <agk@...hat.com>
> > >
> > >  		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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