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Date:   Mon, 3 May 2021 16:54:39 +0300
From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     Frieder Schrempf <frieder.schrempf@kontron.de>
Cc:     Marc Kleine-Budde <mkl@pengutronix.de>, linux-can@vger.kernel.org,
        Wolfgang Grandegger <wg@grandegger.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Timo =?iso-8859-1?B?U2NobPzfbGVy?= <schluessler@krause.de>,
        Tim Harvey <tharvey@gateworks.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: Null pointer dereference in mcp251x driver when resuming from
 sleep
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 <YI//GqCv0nkvtQ54@smile.fi.intel.com>
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On Mon, May 03, 2021 at 04:48:10PM +0300, Andy Shevchenko wrote:
> On Mon, May 03, 2021 at 04:44:24PM +0300, Andy Shevchenko wrote:
> > On Mon, May 03, 2021 at 03:11:40PM +0200, Frieder Schrempf wrote:
> > > Hi,
> > > 
> > > with kernel 5.10.x and 5.12.x I'm getting a null pointer dereference
> > > exception from the mcp251x driver when I resume from sleep (see trace
> > > below).
> > > 
> > > As far as I can tell this was working fine with 5.4. As I currently don't
> > > have the time to do further debugging/bisecting, for now I want to at least
> > > report this here.
> > > 
> > > Maybe there is someone around who could already give a wild guess for what
> > > might cause this just by looking at the trace/code!?
> > 
> > Does revert of c7299fea6769 ("spi: Fix spi device unregister flow") help?
> 
> Other than that, bisecting will take not more than 3-4 iterations only:
> % git log --oneline v5.4..v5.10.34 -- drivers/net/can/spi/mcp251x.c
> 3292c4fc9ce2 can: mcp251x: fix support for half duplex SPI host controllers
> e0e25001d088 can: mcp251x: add support for half duplex controllers
> 74fa565b63dc can: mcp251x: Use readx_poll_timeout() helper
> 2d52dabbef60 can: mcp251x: add GPIO support
> cfc24a0aa7a1 can: mcp251x: sort include files alphabetically
> df561f6688fe treewide: Use fallthrough pseudo-keyword

> 8ce8c0abcba3 can: mcp251x: only reset hardware as required

And only smoking gun by analyzing the code is the above. So, for the first I
would simply check before that commit and immediately after (15-30 minutes of
work). (I would do it myself if I had a hardware at hand...)

> 877a902103fd can: mcp251x: add mcp251x_write_2regs() and make use of it
> 50ec88120ea1 can: mcp251x: get rid of legacy platform data
> 14684b93019a Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

-- 
With Best Regards,
Andy Shevchenko