Date: Sun, 9 Nov 2014 16:36:44 +0100
From: Philipp Zabel <pza@pengutronix.de>
To: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Cc: Philipp Zabel <p.zabel@pengutronix.de>,
        Grant Likely <grant.likely@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        devel@driverdev.osuosl.org,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Mauro Carvalho Chehab <m.chehab@samsung.com>,
        Russell King <rmk+kernel@arm.linux.org.uk>, kernel@pengutronix.de
Subject: Re: [PATCH v5 1/6] of: Decrement refcount of previous endpoint in
 of_graph_get_next_endpoint
Message-ID: <20141109153644.GA3132@pengutronix.de>
References: <1412013819-29181-1-git-send-email-p.zabel@pengutronix.de>
 <1412013819-29181-2-git-send-email-p.zabel@pengutronix.de>
 <Pine.LNX.4.64.1411072255130.4252@axis700.grange>
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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.

regards
Philipp
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