linux-kernel - Re: [PATCH] i2c: tegra: fix a possible NULL dereference

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Date:	Thu, 12 Nov 2015 14:28:37 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	LABBE Corentin <montjoie.mailing@...il.com>
Cc:	LABBE Corentin <clabbe.montjoie@...il.com>, gnurou@...il.com,
	ldewangan@...dia.com, swarren@...dotorg.org, wsa@...-dreams.de,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org
Subject: Re: [PATCH] i2c: tegra: fix a possible NULL dereference

On Thu, Nov 12, 2015 at 01:54:22PM +0100, LABBE Corentin wrote:
> On Thu, Nov 12, 2015 at 01:29:23PM +0100, Thierry Reding wrote:
> > On Thu, Nov 12, 2015 at 08:26:03AM +0100, LABBE Corentin wrote:
> > > of_match_device could return NULL, and so cause a NULL pointer
> > 
> > No. There is no way that of_match_device() can ever fail. The driver
> > core uses the same table to match the OF device to the driver, so the
> > only case where of_match_device() would return NULL is if no match was
> > found, in which case the tegra_i2c_probe() function would never have
> > been called in the first place.
> > 
> > Thierry
> > 
> 
> In a parallel thread for i2c-rcar, the conclusion was different.
> https://lkml.org/lkml/2015/11/12/83

The conclusion was the same: there should be no case where this happens.
The example that Uwe gave is hypothetical and not valid DT in the first
place. So instead of chickening out I think it'd be better to just crash
to make sure people fix the DT.

On a side-note I think that platform_match() should be stricter and do
something like this instead:

	if (dev->of_node) {
		if (of_driver_match_device(dev, drv))
			return 1;

		return 0;
	}

Thierry

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