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Message-ID: <Pine.LNX.4.64.1411091651210.17370@axis700.grange>
Date: Sun, 9 Nov 2014 16:51:42 +0100 (CET)
From: Guennadi Liakhovetski <g.liakhovetski@....de>
To: Philipp Zabel <pza@...gutronix.de>
cc: Philipp Zabel <p.zabel@...gutronix.de>,
Grant Likely <grant.likely@...aro.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
devel@...verdev.osuosl.org,
Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Mauro Carvalho Chehab <m.chehab@...sung.com>,
Russell King <rmk+kernel@....linux.org.uk>,
kernel@...gutronix.de
Subject: Re: [PATCH v5 1/6] of: Decrement refcount of previous endpoint in
of_graph_get_next_endpoint
On Sun, 9 Nov 2014, Philipp Zabel wrote:
> Hi Guennadi,
>
> On Fri, Nov 07, 2014 at 11:06:21PM +0100, Guennadi Liakhovetski wrote:
> > Hi Philipp,
> >
> > Thanks for the patch and sorry for a late reply. I did look at your
> > patches earlier too, but maybe not attentively enough, or maybe I'm
> > misunderstanding something now. In the scan_of_host() function in
> > soc_camera.c as of current -next I see:
> >
> > epn = of_graph_get_next_endpoint(np, epn);
> >
> > which already looks like a refcount leak to me. If epn != NULL, its
> > refcount is incremented, but then immediately the variable gets
> > overwritten, and there's no extra copy of that variable to fix this. If
> > I'm right, then that bug in itself should be fixed, ideally before your
> > patch is applied. But in fact, your patch fixes this, since it modifies
> > of_graph_get_next_endpoint() to return with prev's refcount not
> > incremented, right? Whereas the of_node_put(epn) later down in
> > scan_of_host() decrements refcount of the _next_ endpoint, not the
> > previous one, so, it should be left alone? I.e. AFAICT your modification
> > to of_graph_get_next_endpoint() fixes soc_camera.c with no further
> > modifications to it required?
>
> You are right. With the old implementation, you'd have to do the
> epn = of_graph_get_next_endpoint(np, prev); of_node_put(prev); prev = epn;
> dance to avoid leaking a reference to the first endpoint. This series
> accidentally fixes soc_camera by changing of_graph_get_next_endpoint
> to decrement the reference count itself.
Right, so, the patch has to be adjusted not to touch soc_camera.c at all.
Thanks
Guennadi
>
> regards
> Philipp
>
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