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

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Date:   Tue, 16 Feb 2021 08:53:42 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     peterhuewe@....de, jarkko@...nel.org, 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 01:31:00AM +0100, Lino Sanfilippo wrote:
>  
> +static int tpm_add_tpm2_char_device(struct tpm_chip *chip)
> +{
> +	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;
> +	/*
> +	 * 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);
> +	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

Jason