netdev - Re: [rds-devel] [PATCH] rds: prevent BUG_ON triggering on congestion map updates

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Date:	Mon, 7 Mar 2011 15:56:30 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	rds-devel <rds-devel@....oracle.com>,
	Venkat Venkatsubra <venkat.x.venkatsubra@...cle.com>
Subject: Re: [rds-devel] [PATCH] rds: prevent BUG_ON triggering on congestion
 map updates

On Mon, Mar 07, 2011 at 03:41:04PM -0500, Chris Mason wrote:
> Excerpts from David Miller's message of 2011-03-07 15:27:53 -0500:
> > From: Neil Horman <nhorman@...driver.com>
> > Date: Wed,  2 Mar 2011 11:28:22 -0500
> > 
> > > Recently had this bug halt reported to me:
> > 
> > Well, does anyone on the RDS team care about this bug fix at all?
> > 
> > Stuff like this should not sit for nearly a week without any reply
> > whatsoever.
> > 
> 
> The patch looks good to me, but I'm surprised we haven't seen it here.
> Venkat please take a look (link to the patch below)  Has it only been seen on ppc?
> 
Yes, its only been observed on ppc64.  Its does seem like it should be
observable on other arches.  I presumed it had something to do with ppc64
alignment and how it filled in the sg array, that led to a leftover bit of space
in the scattergather array.  Honestly though I wasnt too worried about ferreting
out the source, since it seemed apparent to me that buffers with
RDS_FLAG_CONG_BITMAP set were just causing rds_[loop|ib]_xmit to return a dummy
positive value (I say dummy because theres no actual data transmitted).  So I
figured if the value is just there to satisfy the return code, it might as well
also satisfy what is otherwise a valid BUG_ON check too.

Best
Neil

> http://permalink.gmane.org/gmane.linux.network/187933
> 
> -chris
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