linux-kernel - RE: [PATCH 1/2] Drivers: hv: balloon: Fix a bug in the hot-add code

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Message-ID: <a53af503f3934a6bb8442e97de0d5ddc@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Fri, 12 Jul 2013 21:07:19 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Ben Hutchings <ben@...adent.org.uk>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	Stable <stable@...r.kernel.org>
Subject: RE: [PATCH 1/2] Drivers: hv: balloon: Fix a bug in the hot-add code



> -----Original Message-----
> From: Ben Hutchings [mailto:ben@...adent.org.uk]
> Sent: Friday, July 12, 2013 4:17 PM
> To: KY Srinivasan
> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> jasowang@...hat.com; Stable
> Subject: Re: [PATCH 1/2] Drivers: hv: balloon: Fix a bug in the hot-add code
> 
> On Fri, Jul 12, 2013 at 06:56:14AM -0700, K. Y. Srinivasan wrote:
> > As we hot-add 128 MB chunks of memory, we wait to ensure that the memory
> > is onlined before attempting to hot-add the next chunk. If the udev rule for
> > memory hot-add is not executed within the allowed time, we would rollback
> the
> > state and abort further hot-add. Since the hot-add has succeeded and the only
> > failure is that the memory is not onlined within the allowed time, we should not
> > be rolling back the state. Fix this bug.
> [...]
> >  		/*
> >  		 * Wait for the memory block to be onlined.
> >  		 */
> > -		t = wait_for_completion_timeout(&dm_device.ol_waitevent,
> 5*HZ);
> > -		if (t == 0) {
> > -			pr_info("hot_add memory timedout\n");
> > -			has->ha_end_pfn -= HA_CHUNK;
> > -			has->covered_end_pfn -=  processed_pfn;
> > -			break;
> > -		}
> > +		wait_for_completion_timeout(&dm_device.ol_waitevent,
> 5*HZ);
> >
> >  	}
> >
> 
> Well now it might look like a bug that you don't test the result
> of wait_for_completion_timeout().  Maybe update the comment to
> explain why it's OK to continue anyway?

I put in the comment in the patch explaining why it is ok to continue. To reiterate,
it is ok to continue because hot add has succeeded. More importantly, what I was
doing earlier - rolling back the state when in fact hot add had succeeded was incorrect.

Regards,

K. Y
> 
> Ben.
> 
> --
> Ben Hutchings
> We get into the habit of living before acquiring the habit of thinking.
>                                                               - Albert Camus
> 


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