linux-kernel - Re: [PATCH v4] tpm: fix reference counting for struct tpm

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Message-ID: <YCvuS9cIT7umOjhy@kernel.org>
Date:   Tue, 16 Feb 2021 18:09:47 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Lino Sanfilippo <LinoSanfilippo@....de>, peterhuewe@....de,
        stefanb@...ux.vnet.ibm.com, James.Bottomley@...senpartnership.com,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lino Sanfilippo <l.sanfilippo@...bus.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v4] tpm: fix reference counting for struct tpm_chip

On Tue, Feb 16, 2021 at 06:04:42PM +0200, Jarkko Sakkinen wrote:
> On Tue, Feb 16, 2021 at 08:53:42AM -0400, Jason Gunthorpe wrote:
> > On Tue, Feb 16, 2021 at 01:31:00AM +0100, Lino Sanfilippo wrote:
> > >  
> > > +static int tpm_add_tpm2_char_device(struct tpm_chip *chip)
> 
> BTW, this naming is crap.
> 
> - 2x tpm
> - char is useless
> 
> -> tpm2_add_device

Actually, tpm2s_add_device() add put it to tpm2-space.c.

> > > +{
> > > +	int rc;
> > > +
> > > +	device_initialize(&chip->devs);
> > > +	chip->devs.parent = chip->dev.parent;
> > > +	chip->devs.class = tpmrm_class;
> > > +
> > > +	rc = dev_set_name(&chip->devs, "tpmrm%d", chip->dev_num);
> > > +	if (rc)
> > > +		goto out_put_devs;
> 
> Right, and empty line missing here.
> 
> > > +	/*
> > > +	 * get extra reference on main device to hold on behalf of devs.
> > > +	 * This holds the chip structure while cdevs is in use. The
> > > +	 * corresponding put is in the tpm_devs_release.
> > > +	 */
> > > +	get_device(&chip->dev);
> > > +	chip->devs.release = tpm_devs_release;
> > > +	chip->devs.devt =
> > > +		MKDEV(MAJOR(tpm_devt), chip->dev_num + TPM_NUM_DEVICES);
> 
> Isn't this less than 100 chars?
> 
> > > +	cdev_init(&chip->cdevs, &tpmrm_fops);
> > > +	chip->cdevs.owner = THIS_MODULE;
> > > +
> > > +	rc = cdev_device_add(&chip->cdevs, &chip->devs);
> > > +	if (rc) {
> > > +		dev_err(&chip->devs,
> > > +			"unable to cdev_device_add() %s, major %d, minor %d, err=%d\n",
> > > +			dev_name(&chip->devs), MAJOR(chip->devs.devt),
> > > +			MINOR(chip->devs.devt), rc);
> > > +		goto out_put_devs;
> > > +	}
> > > +
> > > +	return 0;
> > > +
> > > +out_put_devs:
> > > +	put_device(&chip->devs);
> > 
> > I'd rather you organize this so chip->devs.release and the get_device
> > is always sent instead of having the possiblity for a put_device that
> > doesn't call release
> 
> /Jarkko