linux-kernel - Re: [tpmdd-devel] [PATCH] tpm: fix rollback/cleanup before tpm_chip

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Date:	Wed, 3 Feb 2016 17:34:37 -0700
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:	Peter Huewe <peterhuewe@....de>, stable@...r.kernel.org,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [tpmdd-devel] [PATCH] tpm: fix rollback/cleanup before
 tpm_chip_register()

On Wed, Feb 03, 2016 at 08:02:35AM -0800, Jarkko Sakkinen wrote:

> Would s/the platform device/the parent device/ be better?

Yes

> > > +	/* Associate character device with the platform device only after
> > > +	 * it is properly initialized.
> > > +	 */
> > > +	dev_set_drvdata(pdev, chip);
> > > +	devm_add_action(pdev, (void (*)(void *)) tpm_dev_release,
> > > &chip->dev);
> > 
> > No, a release function can never be called naked. The action needs
> > to do put_device, which is the error unwind for device_initialize().
> 
> Got it (already from your first comment)!
> 
> What does "called naked" even mean? I just don't understand the
> english here and want to be sure that I understand what you are saying
> and not make false assumptions.

'called naked' would refer to just open coding a call to
tpm_dev_release, using it as a devm_add_action is the same as open
coding.

The function must only ever be called by put_device.

> > > @@ -162,7 +165,10 @@ static int tpm_add_char_device(struct tpm_chip *chip)
> > >  			MINOR(chip->dev.devt), rc);
> > >  
> > >  		cdev_del(&chip->cdev);
> > > -		return rc;
> > > +	} else {
> > > +		devm_remove_action(chip->dev.parent,
> > > +				   (void (*)(void *)) tpm_dev_release,
> > > +				   &chip->dev);
> > 
> > This is in the wrong place, the devm should be canceled only if
> > tpm_chip_register returns success, at that point the caller's contract
> > is to guarentee a call to tpm_chip_unregister, and
> > tpm_chip_unregister does the put_device that calls the release
> > function.
> 
> rc == 0 at that point i.e. success. I don't see the problem here.

It should not be in tpm_add_char_device

I'm also not completely sure about the error handling around
tpm_register - if it fails the tpm_chip should not be destroyed, and I
think it does..

It would probably be ideal to just rely on devm to always do the final
put_device and avoid the devm_remove_action entirely. I think this
means a get_device will be needed in tpm_register after device_add ?
Didn't look closely at how all the refs balance.

Jason