linux-kernel - Re: [PATCH 9/12] repost: cciss: add busy

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Message-ID: <20061213125236.GO4576@kernel.dk>
Date:	Wed, 13 Dec 2006 13:52:36 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Mike Miller (OS Dev)" <mikem@...rdog.cca.cpqcorp.net>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, chase.maupin@...com
Subject: Re: [PATCH 9/12] repost: cciss: add busy_configuring flag

On Tue, Dec 12 2006, Mike Miller (OS Dev) wrote:
> On Mon, Nov 06, 2006 at 09:32:00PM +0100, Jens Axboe wrote:
> > On Mon, Nov 06 2006, Mike Miller (OS Dev) wrote:
> > > PATCH 9 of 12
> > > 
> > > This patch adds a check for busy_configuring to prevent starting a queue
> > > on a drive that may be in the midst of updating, configuring, deleting, etc.
> > > 
> > > This had a test for if the queue was stopped or plugged but that seemed
> > > to cause issues.
> > > Please consider this for inclusion.
> > > 
> > > Thanks,
> > > mikem
> > > 
> > > Signed-off-by: Mike Miller <mike.miller@...com>
> > > 
> > > --------------------------------------------------------------------------------
> > > 
> > > ---
> > > 
> > >  drivers/block/cciss.c |    5 ++++-
> > >  1 files changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff -puN drivers/block/cciss.c~cciss_busy_conf_for_lx2619-rc4 drivers/block/cciss.c
> > > --- linux-2.6/drivers/block/cciss.c~cciss_busy_conf_for_lx2619-rc4	2006-11-06 13:27:53.000000000 -0600
> > > +++ linux-2.6-root/drivers/block/cciss.c	2006-11-06 13:27:53.000000000 -0600
> > > @@ -1190,8 +1190,11 @@ static void cciss_check_queues(ctlr_info
> > >  		/* make sure the disk has been added and the drive is real
> > >  		 * because this can be called from the middle of init_one.
> > >  		 */
> > > -		if (!(h->drv[curr_queue].queue) || !(h->drv[curr_queue].heads))
> > > +		if (!(h->drv[curr_queue].queue) ||
> > > +		    !(h->drv[curr_queue].heads) ||
> > > +		    h->drv[curr_queue].busy_configuring)
> > >  			continue;
> > > +
> > >  		blk_start_queue(h->gendisk[curr_queue]->queue);
> > 
> > This is racy, because you don't start the queue when you unset
> > ->busy_configuring later on. For this to be safe, you need to call
> > blk_start_queue() when you set ->busy_configuring to 0.
> 
> Jens, please see Chase's reply to your concerns:
> > busy_configuring - I do not think this is racy.  This
> > flag is used only when we are removing/deleting a disk.  In
> > this case the queue is cleaned up and the disk is deleted.
> > If we are doing that then there is no queue to start later.
> > The check of this flag in the interrupt handler is to prevent
> > us from trying to start a queue that is in the middle of
> > being deleted.  This flag could be called busy_deleting.

Ok, no worries then if it's simply a going away flag. I wonder if it's
needed at all, but it certainly doesn't hurt.

-- 
Jens Axboe

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