Date: Fri, 27 Nov 2015 11:11:25 +0100
From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
	<u.kleine-koenig@pengutronix.de>
To: martin.wilck@ts.fujitsu.com
Cc: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        tpmdd-devel@lists.sourceforge.net
Subject: Re: [PATCH] base/platform: fix panic when probe function is NULL
Message-ID: <20151127101125.GS19888@pengutronix.de>
References: <1448564494-23218-1-git-send-email-martin.wilck@ts.fujitsu.com>
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Hello Martin,

On Thu, Nov 26, 2015 at 08:01:34PM +0100, martin.wilck@ts.fujitsu.com wrote:
> From: Martin Wilck <Martin.Wilck@ts.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().

Correct, this is an unintended change of behaviour introduced in
b8b2c7d845d5.

> 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 sounds like a separate issue though. Looking at init_tis there is:

        rc = platform_driver_register(&tis_drv);
        if (rc < 0)
                return rc;
        pdev = platform_device_register_simple("tpm_tis", -1, NULL, 0);
        if (IS_ERR(pdev)) {
                rc = PTR_ERR(pdev);
                goto err_dev;
        }
        rc = tpm_tis_init(&pdev->dev, &tis_default_info, NULL);

tpm_tis_init calls tpmm_chip_alloc which barfs when pdev (i.e. the return value
of platform_device_register_simple above) isn't bound. It is not allowed
to assume that the device is bound after the above function calls.

So I'd say drop the paragraph about tpm_tis and the change is fine.

> 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")
> 

I think line breaks in the Fixes: line are frowned on. Also usually
there is no empty line between Fixes: and S-o-b:.

> Signed-off-by: Martin Wilck <Martin.Wilck@ts.fujitsu.com>
> ---
>  drivers/base/platform.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 1dd6d3b..c994e76 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -513,10 +513,14 @@ static int platform_drv_probe(struct device *_dev)
>  		return ret;
>  
>  	ret = dev_pm_domain_attach(_dev, true);
> -	if (ret != -EPROBE_DEFER && drv->probe) {
> -		ret = drv->probe(dev);
> -		if (ret)
> -			dev_pm_domain_detach(_dev, true);
> +	if (ret != -EPROBE_DEFER) {
> +		if (drv->probe) {
> +			ret = drv->probe(dev);
> +			if (ret)
> +				dev_pm_domain_detach(_dev, true);
> +		} else
> +			/* don't fail if just dev_pm_domain_attach failed */
> +			ret = 0;

An else that has a } should also have a {, according to 
checkpatch and Documentation/CodingStyle. You can write it
alternatively as:

	if (ret != -EPROBE_DEFER) {
		if (drv->probe)
			ret = drv->probe(dev);
		else
			ret = 0;

		if (ret)
			dev_pm_domain_detach(_dev, true);
	}

.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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