linux-kernel - Re: [tpmdd-devel] [PATCH] base/platform: fix panic when probe function is NULL

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Date:	Mon, 30 Nov 2015 14:56:31 +0200
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	martin.wilck@...fujitsu.com, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, tpmdd-devel@...ts.sourceforge.net
Subject: Re: [tpmdd-devel] [PATCH] base/platform: fix panic when probe
 function is NULL

Hi Uwe,

On Sun, Nov 29, 2015 at 10:54:11AM +0100, Uwe Kleine-König wrote:
> Hello Jarkko,
> 
> On Sat, Nov 28, 2015 at 06:34:47PM +0200, Jarkko Sakkinen wrote:
> > On Thu, Nov 26, 2015 at 08:01:34PM +0100, martin.wilck@...fujitsu.com wrote:
> > > From: Martin Wilck <Martin.Wilck@...fujitsu.com>
> > > 
> > > Since b8b2c7d845d5, platform_drv_probe() is called for all platform
> > > devices. If drv->probe is NULL, and dev_pm_domain_attach() fails,
> > > platform_drv_probe() will return the error code from dev_pm_domain_attach().
> > > 
> > > This causes real_probe() to enter the "probe_failed" path and set
> > > dev->driver to NULL. Before b8b2c7d845d5, real_probe() would assume
> > > success if both dev->bus->probe and drv->probe are missing.
> > > 
> > > This may cause a panic later. For example, inserting the tpm_tis
> > > driver with parameter "force=1" (i.e. registering tpm_tis as a platform
> > > driver) will panic in tpmm_chip_alloc() because dev->driver is NULL:
> > > 
> > >      chip->cdev.owner = chip->pdev->driver->owner;
> > > 
> > > This patch fixes this by returning success in platform_drv_probe() if
> > > "just" dev_pm_domain_attach() had failed. This restores the semantics
> > > of platform_device_register_XXX() if the associated platform driver has
> > > no "probe" function.
> > > 
> > > Fixes: b8b2c7d845d5 ("base/platform: assert that dev_pm_domain
> > > callbacks are called unconditionally")
> > > 
> > > Signed-off-by: Martin Wilck <Martin.Wilck@...fujitsu.com>
> > 
> > Acked-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> 
> While the patch is fine, the commit log is not. It blames b8b2c7d845d5
> to be responsible for a panic, but in fact it only breaks the wrong
> assumption of the tpm_tis driver.
> 
> So I'm not sure how to interpret your Ack, IMHO it should not make
> gregkh pick up the patch as is.

Alright. I don't think you can speak about *wrong assumptions* if the
semantics allowed not to have it before. *Where* it should be fixed is
another question. I'd keep the Fixes tag in all cases.

Jason, you had the fix for this issue directly to tpm_tis driver that
you haven't yet posted, right? Just double-checking this.

> Best regards
> Uwe
> 
> -- 
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |

/Jarkko
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