linux-kernel - Re: [PATCH] Fix guest memory leak and panic

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Message-ID: <OFF9A5DA76.A2860DAC-ON6525792D.0039157B-6525792D.00396BDE@in.ibm.com>
Date:	Tue, 18 Oct 2011 15:58:52 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
Cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH] Fix guest memory leak and panic

Ian Campbell <Ian.Campbell@...rix.com> wrote on 10/18/2011 02:06:56 PM:

Hi Ian,

> On Tue, 2011-10-18 at 09:05 +0100, Krishna Kumar wrote:
> > The extra reference to the fragment pages causes those pages to
> > not get freed in skb_release_data(). The following patch fixes
> > the bug. I have not checked if any other converted driver has
> > the same issue.
>
> Damn. You are completely correct and I appear to have made this same
> mistake several times. A quick look suggests that at least cxbg,
> myriage, vmxnet, cassini and bnx2 may potentially have a similar
> issue :-( (I stopped looking at that point, I'll obviously do a full
> audit).
>
> I considered quite carefully whether (__)skb_frag_set_page should take a
> reference or not and decided yes but I'm starting to reconsider whether
> I made the right choice. It seems that is just confusing and violates
> the principal of least surprise to have a function called "set" take a
> new reference. In reality all existing drivers expect that adding a page
> to an SKB frag will just take over the existing reference.
>
> I think the best thing might be to remove the additional ref taking from
> the setter function and audit the previous changes to ensure they
> conform. I'll do that right away and post a fixup patch ASAP.
>
> > Signed-off-by: Krishna Kumar <krkumar2@...ibm.com>
>
> This change is correct as things stand today, so:
>
> Acked-by: Ian Campbell <ian.campbell@...rix.com>
>
> but perhaps it would be better to hold off and let me fix all of these
> all at once.

Either way is fine with me. However, besides having a fix,
I would like to remove the manual initializations in
set_skb_frag(), and substitute with __skb_fill_page_desc,
like other drivers do.

thanks,

- KK

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