linux-kernel - Re: [patch] cciss: Fix race between disk-adding code and interrupt handler

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Message-ID: <20080414172716.GM16584@beardog.cca.cpqcorp.net>
Date:	Mon, 14 Apr 2008 12:27:16 -0500
From:	scameron@...rdog.cca.cpqcorp.net
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org, mike.miller@...com,
	mikem@...rdog.cca.cpqcorp.net, scameron@...rdog.cca.cpqcorp.net
Subject: Re: [patch] cciss: Fix race between disk-adding code and interrupt handler



> On Mon, Apr 14 2008, scameron@...rdog.cca.cpqcorp.net wrote:
> > 
> > 
> > Fix race condition between cciss_init_one(), cciss_update_drive_info(),
> > and cciss_check_queues().  cciss_softirq_done would try to start
> > queues which were not quite ready to be started, as its checks for
> > readiness were not sufficiently synchronized with the queue initializing
> > code in cciss_init_one and cciss_update_drive_info.  Slow cpu and
> > large numbers of logical drives seem to make the race more likely 
> > to cause a problem.
> 
> Hmm, this seems backwards to me.  cciss_softirq_done() isn't going to
> start the queues, until an irq has triggered for instance. Why isn't the
> init properly ordered instead of band-aiding around this with a
> 'queue_ready' variable?
>

Each call to add_disk() will trigger some interrupts, 
and earlier added disks may cause the queues of later,
not-yet-completely added disks to be started.

I suppose the init routine might be reorganized to initialize all
the queues, then have second loop call add_disk() for all
of them.  Is that what you had in mind by "properly ordered?"

Disks may be added at run time though, and I think this tears
down all but the first disk, and re-adds them all, if I remember
right, so there is some complication there to think about.

-- steve

On Mon, Apr 14, 2008 at 07:05:05PM +0200, Jens Axboe wrote:
> -- 
> Jens Axboe
> 
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