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

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Date:	Mon, 30 Nov 2015 15:06:50 +0200
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	gregkh@...uxfoundation.org, tpmdd-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [tpmdd-devel] [PATCH] base/platform: fix panic when probe
 function is NULL

On Mon, Nov 30, 2015 at 02:56:31PM +0200, Jarkko Sakkinen wrote:
> 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.

Uwe, please ignore this :) Saw your more in-depth comment about platform
driver creation. Thank you. I somehow have missed it before.

/Jarkko
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