linux-kernel - Re: [PATCH 1/2] resubmit cciss: kernel thread to detect changes on MSA2012

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Date:	Fri, 6 Mar 2009 15:56:23 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Mike Miller (OS Dev)" <mikem@...rdog.cca.cpqcorp.net>
Cc:	James.Bottomley@...senPartnership.com, mike.miller@...com,
	jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, coldwell@...hat.com
Subject: Re: [PATCH 1/2] resubmit cciss: kernel thread to detect changes on
 MSA2012

On Fri, 6 Mar 2009 17:29:18 -0600
"Mike Miller (OS Dev)" <mikem@...rdog.cca.cpqcorp.net> wrote:

> On Fri, Mar 06, 2009 at 12:24:27PM -0600, James Bottomley wrote:
> > On Fri, 2009-03-06 at 12:16 -0600, Mike Miller wrote:
> > > Patch 1 of 2
> > > 
> > > This is a resubmission of yesterdays patch to detect changes on the MSA2012.
> > > I hope I've addressed all concerns. This patch rearranges some of the code
> > > so we also have coverage in the sg and the ioctl paths as well as the main
> > > data path.
> > > 
> > > The MSA2012 cannot inform the driver of configuration changes since all
> > > management is out of band. This is a departure from any storage we have
> > > supported in the past. We need some way to detect changes on the topology so
> > > we implement this kernel thread. In some instances there's nothing we can do
> > > from the driver (like LUN failure) so just print out a message. In the case
> > > where logical volumes are added or deleted we call rebuild_lun_table to
> > > refreash the driver's view of the world.
> > > 
> > > Please consider this for inclusion.
> > 
> > I still don't quite see how the thread stops on module removal ... there
> > needs to be an explicit kthread_stop() somewhere in the clean up path.
> > 
> > James
> > 
> > 
> This time I make a call to kthread_stop in cciss_remove_one. The driver can
> be unloaded and the thread gets cleaned up.

Please include a complete (and suitably updated) copy of the changelog
with each iteration of a patch.


> KNOWN BUG: it seems the timeout must expire before kthread_stop actually
> stops the thread. This causes the driver to hang and wait during rmmod. I've
> played around with several things but haven't found the correct way to
> address the problem. Looking at other drivers hasn't been much help. Any
> advice is greatly appreciated.

Well, wait_for_completion_timeout() is only going to return when the
timeout timed out, or someone ran complete().

> +static int scan_thread(ctlr_info_t *h)
> +{
> +	int rc;
> +	DECLARE_COMPLETION_ONSTACK(wait);
> +	h->rescan_wait = &wait;
> +
> +	while (!kthread_should_stop()) {
> +		rc = wait_for_completion_timeout(&wait, 300 * HZ);
> +		if (!rc)
> +			continue;
> +		else
> +			rebuild_lun_table(h, 0);
> +	}
> +	return 0;
> +}

So..  we shouldn't need the timeout here at all - just use
wait_for_completion().

static int scan_thread(ctlr_info_t *h)
{
	DECLARE_COMPLETION_ONSTACK(wait);

	h->rescan_wait = &wait;
	for ( ; ; ) {
		wait_for_completion(&wait);
		if (kthread_should_stop())
			break;
		rebuild_lun_table(h, 0);
	}
	return 0;
}

And on the teardown path, do

	complete(...);
	kthread_stop(...);

?
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