linux-kernel - Re: [PATCH] base: dd: don't remove driver_data in -EPROBE

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Date:	Tue, 3 May 2016 17:14:59 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Yi Zhang <yizhang_hust@....com>, linux-kernel@...r.kernel.org,
	linux-tegra@...r.kernel.org
Subject: Re: [PATCH] base: dd: don't remove driver_data in -EPROBE_DEFER case

On Tue, May 03, 2016 at 08:07:39AM -0700, Greg KH wrote:
> On Tue, May 03, 2016 at 03:11:26PM +0200, Thierry Reding wrote:
> > On Tue, Mar 08, 2016 at 11:15:22PM +0800, Yi Zhang wrote:
> > > the driver_data may be used for sanity check, it fails the
> > > probe() if driver_data is NULL after it is re-triggered.
> > > for example, soc_probe() in sound/soc/soc-core.c
> > > 
> > > Signed-off-by: Yi Zhang <yizhang_hust@....com>
> > > ---
> > >  drivers/base/dd.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > Hi Greg,
> > 
> > This causes a boot regression on at least one board, caused by one of
> > the drivers looking at driver data to check whether or not the driver
> > has properly loaded. If the code encounters a non-NULL pointer it
> > tries to dereference it, but because it's already been freed there is
> > no memory backing it and things crash.
> > 
> > I don't think keeping stale pointers around is a good idea. The whole
> > point of setting this to NULL in the core is so that probe failures
> > result in the same starting conditions no matter what.
> > 
> > Can we please get this reverted?
> > 
> > Cc'ing linux-tegra for visibility since that's where the boot regression
> > is observed.
> 
> Now reverted, thanks for letting me know.

Thanks Greg.

Thierry

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