Date:	Mon, 7 Oct 2013 09:38:13 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [DMA-API] BUG: unable to handle kernel NULL pointer
	dereference at 0000000000000248

Fengguang,

Have you done anything with this at all?  If not, don't expect me to
sort this out, because I can't test this.  Thanks.

On Fri, Oct 04, 2013 at 11:41:36AM +0100, Russell King - ARM Linux wrote:
> On Fri, Oct 04, 2013 at 09:40:17AM +0800, Fengguang Wu wrote:
> > This BUG does not show up in upstream and linux-next, so either the
> > commit has not been merged or has been fixed somewhere.
> 
> That's because I haven't pushed it out into linux-next yet.  Thanks
> for testing nevertheless.
> 
> > [  267.537083] sdhci-pltfm: SDHCI platform and OF driver helper
> > [  267.602219] ledtrig-cpu: registered to indicate activity on CPUs
> > [  267.656654] BUG: unable to handle kernel NULL pointer dereference at 0000000000000248
> > [  267.656689] IP: [<ffffffff810073c9>] dma_supported+0x9/0xa0
> 
> This seems to be saying that 'dev' was approximately a NULL pointer.
> 
> This is a wonderfully written driver this is... it's not really a
> platform driver at all.  It stores the platform device into the global
> dcdbas_pdev, and then references it from within the driver.  The problem
> is caused by that happening before platform_device_register_full() has
> returned and stored the platform device pointer.  It's use of a
> platform device is just to be able to have some sysfs attributes which
> it can play around with (I wonder if anyone has reviewed what it does
> with these...)
> 
> You can also find goodies like this here:
> 
>         /*
>          * We have to free the buffer here instead of dcdbas_remove
>          * because only in module exit function we can be sure that
>          * all sysfs attributes belonging to this module have been
>          * released.
>          */
>         smi_data_buf_free();
>         platform_device_unregister(dcdbas_pdev);
>         platform_driver_unregister(&dcdbas_driver);
> 
> which is quite a statement in itself, and if it's thought about, how
> can putting smi_data_buf_free() before platform_device_unregister()
> here satisfy that comment.
> 
> Well, short of dropping the patch, I think the easiest solution here is
> this, which annoyingly makes the mess slightly worse:
> 
> diff --git a/drivers/firmware/dcdbas.c b/drivers/firmware/dcdbas.c
> index a85fda2..0a751bf 100644
> --- a/drivers/firmware/dcdbas.c
> +++ b/drivers/firmware/dcdbas.c
> @@ -545,6 +545,8 @@ static int dcdbas_probe(struct platform_device *dev)
>  	host_control_action = HC_ACTION_NONE;
>  	host_control_smi_type = HC_SMITYPE_NONE;
>  
> +	dcdbas_pdev = dev;
> +
>  	/*
>  	 * BIOS SMI calls require buffer addresses be in 32-bit address space.
>  	 * This is done by setting the DMA mask below.
> @@ -588,6 +590,8 @@ static const struct platform_device_info dcdbas_dev_info __initdata = {
>  	.dma_mask	= DMA_BIT_MASK(32),
>  };
>  
> +static struct platform_device *dcdbas_pdev_reg;
> +
>  /**
>   * dcdbas_init: initialize driver
>   */
> @@ -599,9 +603,9 @@ static int __init dcdbas_init(void)
>  	if (error)
>  		return error;
>  
> -	dcdbas_pdev = platform_device_register_full(&dcdbas_dev_info);
> -	if (IS_ERR(dcdbas_pdev)) {
> -		error = PTR_ERR(dcdbas_pdev);
> +	dcdbas_pdev_reg = platform_device_register_full(&dcdbas_dev_info);
> +	if (IS_ERR(dcdbas_pdev_reg)) {
> +		error = PTR_ERR(dcdbas_pdev_reg);
>  		goto err_unregister_driver;
>  	}
>  
> @@ -629,8 +633,9 @@ static void __exit dcdbas_exit(void)
>  	 * all sysfs attributes belonging to this module have been
>  	 * released.
>  	 */
> -	smi_data_buf_free();
> -	platform_device_unregister(dcdbas_pdev);
> +	if (dcdbas_pdev)
> +		smi_data_buf_free();
> +	platform_device_unregister(dcdbas_pdev_reg);
>  	platform_driver_unregister(&dcdbas_driver);
>  }
> 
> Another is to try and pull the direct references to dcdbas_pdev up the
> call chains... that's easier said than done because there is a global
> function in this driver - dcdbas_smi_request.  The best I can get to
> is the below, which leaves three direct uses of dcdbas_pdev:
> 
> diff --git a/drivers/firmware/dcdbas.c b/drivers/firmware/dcdbas.c
> index a85fda2..d9d215c 100644
> --- a/drivers/firmware/dcdbas.c
> +++ b/drivers/firmware/dcdbas.c
> @@ -58,15 +58,15 @@ static unsigned int host_control_on_shutdown;
>  /**
>   * smi_data_buf_free: free SMI data buffer
>   */
> -static void smi_data_buf_free(void)
> +static void smi_data_buf_free(struct device *dev)
>  {
>  	if (!smi_data_buf)
>  		return;
>  
> -	dev_dbg(&dcdbas_pdev->dev, "%s: phys: %x size: %lu\n",
> +	dev_dbg(dev, "%s: phys: %x size: %lu\n",
>  		__func__, smi_data_buf_phys_addr, smi_data_buf_size);
>  
> -	dma_free_coherent(&dcdbas_pdev->dev, smi_data_buf_size, smi_data_buf,
> +	dma_free_coherent(dev, smi_data_buf_size, smi_data_buf,
>  			  smi_data_buf_handle);
>  	smi_data_buf = NULL;
>  	smi_data_buf_handle = 0;
> @@ -77,7 +77,7 @@ static void smi_data_buf_free(void)
>  /**
>   * smi_data_buf_realloc: grow SMI data buffer if needed
>   */
> -static int smi_data_buf_realloc(unsigned long size)
> +static int smi_data_buf_realloc(struct device *dev, unsigned long size)
>  {
>  	void *buf;
>  	dma_addr_t handle;
> @@ -89,10 +89,9 @@ static int smi_data_buf_realloc(unsigned long size)
>  		return -EINVAL;
>  
>  	/* new buffer is needed */
> -	buf = dma_alloc_coherent(&dcdbas_pdev->dev, size, &handle, GFP_KERNEL);
> +	buf = dma_alloc_coherent(dev, size, &handle, GFP_KERNEL);
>  	if (!buf) {
> -		dev_dbg(&dcdbas_pdev->dev,
> -			"%s: failed to allocate memory size %lu\n",
> +		dev_dbg(dev, "%s: failed to allocate memory size %lu\n",
>  			__func__, size);
>  		return -ENOMEM;
>  	}
> @@ -102,7 +101,7 @@ static int smi_data_buf_realloc(unsigned long size)
>  		memcpy(buf, smi_data_buf, smi_data_buf_size);
>  
>  	/* free any existing buffer */
> -	smi_data_buf_free();
> +	smi_data_buf_free(dev);
>  
>  	/* set up new buffer for use */
>  	smi_data_buf = buf;
> @@ -110,7 +109,7 @@ static int smi_data_buf_realloc(unsigned long size)
>  	smi_data_buf_phys_addr = (u32) virt_to_phys(buf);
>  	smi_data_buf_size = size;
>  
> -	dev_dbg(&dcdbas_pdev->dev, "%s: phys: %x size: %lu\n",
> +	dev_dbg(dev, "%s: phys: %x size: %lu\n",
>  		__func__, smi_data_buf_phys_addr, smi_data_buf_size);
>  
>  	return 0;
> @@ -141,7 +140,7 @@ static ssize_t smi_data_buf_size_store(struct device *dev,
>  
>  	/* make sure SMI data buffer is at least buf_size */
>  	mutex_lock(&smi_data_lock);
> -	ret = smi_data_buf_realloc(buf_size);
> +	ret = smi_data_buf_realloc(dev, buf_size);
>  	mutex_unlock(&smi_data_lock);
>  	if (ret)
>  		return ret;
> @@ -166,6 +165,7 @@ static ssize_t smi_data_write(struct file *filp, struct kobject *kobj,
>  			      struct bin_attribute *bin_attr,
>  			      char *buf, loff_t pos, size_t count)
>  {
> +	struct device *dev = kobj_to_dev(kobj);
>  	ssize_t ret;
>  
>  	if ((pos + count) > MAX_SMI_DATA_BUF_SIZE)
> @@ -173,7 +173,7 @@ static ssize_t smi_data_write(struct file *filp, struct kobject *kobj,
>  
>  	mutex_lock(&smi_data_lock);
>  
> -	ret = smi_data_buf_realloc(pos + count);
> +	ret = smi_data_buf_realloc(dev, pos + count);
>  	if (ret)
>  		goto out;
>  
> @@ -199,7 +199,7 @@ static ssize_t host_control_action_store(struct device *dev,
>  
>  	/* make sure buffer is available for host control command */
>  	mutex_lock(&smi_data_lock);
> -	ret = smi_data_buf_realloc(sizeof(struct apm_cmd));
> +	ret = smi_data_buf_realloc(dev, sizeof(struct apm_cmd));
>  	mutex_unlock(&smi_data_lock);
>  	if (ret)
>  		return ret;
> @@ -347,7 +347,7 @@ EXPORT_SYMBOL(dcdbas_smi_request);
>   *
>   * Caller must set up the host control command in smi_data_buf.
>   */
> -static int host_control_smi(void)
> +static int host_control_smi(struct device *dev)
>  {
>  	struct apm_cmd *apm_cmd;
>  	u8 *data;
> @@ -426,7 +426,7 @@ static int host_control_smi(void)
>  		break;
>  
>  	default:
> -		dev_dbg(&dcdbas_pdev->dev, "%s: invalid SMI type %u\n",
> +		dev_dbg(dev, "%s: invalid SMI type %u\n",
>  			__func__, host_control_smi_type);
>  		return -ENOSYS;
>  	}
> @@ -443,7 +443,7 @@ static int host_control_smi(void)
>   * use smi_data_buf at this point because the system has finished
>   * shutting down and no userspace apps are running.
>   */
> -static void dcdbas_host_control(void)
> +static void dcdbas_host_control(struct device *dev)
>  {
>  	struct apm_cmd *apm_cmd;
>  	u8 action;
> @@ -455,13 +455,12 @@ static void dcdbas_host_control(void)
>  	host_control_action = HC_ACTION_NONE;
>  
>  	if (!smi_data_buf) {
> -		dev_dbg(&dcdbas_pdev->dev, "%s: no SMI buffer\n", __func__);
> +		dev_dbg(dev, "%s: no SMI buffer\n", __func__);
>  		return;
>  	}
>  
>  	if (smi_data_buf_size < sizeof(struct apm_cmd)) {
> -		dev_dbg(&dcdbas_pdev->dev, "%s: SMI buffer too small\n",
> -			__func__);
> +		dev_dbg(dev, "%s: SMI buffer too small\n", __func__);
>  		return;
>  	}
>  
> @@ -472,12 +471,12 @@ static void dcdbas_host_control(void)
>  		apm_cmd->command = ESM_APM_POWER_CYCLE;
>  		apm_cmd->reserved = 0;
>  		*((s16 *)&apm_cmd->parameters.shortreq.parm[0]) = (s16) 0;
> -		host_control_smi();
> +		host_control_smi(dev);
>  	} else if (action & HC_ACTION_HOST_CONTROL_POWERCYCLE) {
>  		apm_cmd->command = ESM_APM_POWER_CYCLE;
>  		apm_cmd->reserved = 0;
>  		*((s16 *)&apm_cmd->parameters.shortreq.parm[0]) = (s16) 20;
> -		host_control_smi();
> +		host_control_smi(dev);
>  	}
>  }
>  
> @@ -495,7 +494,7 @@ static int dcdbas_reboot_notify(struct notifier_block *nb, unsigned long code,
>  			/* firmware is going to perform host control action */
>  			printk(KERN_WARNING "Please wait for shutdown "
>  			       "action to complete...\n");
> -			dcdbas_host_control();
> +			dcdbas_host_control(&dcdbas_pdev->dev);
>  		}
>  		break;
>  	}
> @@ -545,11 +544,13 @@ static int dcdbas_probe(struct platform_device *dev)
>  	host_control_action = HC_ACTION_NONE;
>  	host_control_smi_type = HC_SMITYPE_NONE;
>  
> +	dcdbas_pdev = dev;
> +
>  	/*
>  	 * BIOS SMI calls require buffer addresses be in 32-bit address space.
>  	 * This is done by setting the DMA mask below.
>  	 */
> -	error = dma_set_coherent_mask(&dcdbas_pdev->dev, DMA_BIT_MASK(32));
> +	error = dma_set_coherent_mask(&dev->dev, DMA_BIT_MASK(32));
>  	if (error)
>  		return error;
>  
> @@ -588,6 +589,8 @@ static const struct platform_device_info dcdbas_dev_info __initdata = {
>  	.dma_mask	= DMA_BIT_MASK(32),
>  };
>  
> +static struct platform_device *dcdbas_pdev_reg;
> +
>  /**
>   * dcdbas_init: initialize driver
>   */
> @@ -599,9 +602,9 @@ static int __init dcdbas_init(void)
>  	if (error)
>  		return error;
>  
> -	dcdbas_pdev = platform_device_register_full(&dcdbas_dev_info);
> -	if (IS_ERR(dcdbas_pdev)) {
> -		error = PTR_ERR(dcdbas_pdev);
> +	dcdbas_pdev_reg = platform_device_register_full(&dcdbas_dev_info);
> +	if (IS_ERR(dcdbas_pdev_reg)) {
> +		error = PTR_ERR(dcdbas_pdev_reg);
>  		goto err_unregister_driver;
>  	}
>  
> @@ -629,8 +632,9 @@ static void __exit dcdbas_exit(void)
>  	 * all sysfs attributes belonging to this module have been
>  	 * released.
>  	 */
> -	smi_data_buf_free();
> -	platform_device_unregister(dcdbas_pdev);
> +	if (dcdbas_pdev)
> +		smi_data_buf_free(&dcdbas_pdev->dev);
> +	platform_device_unregister(dcdbas_pdev_reg);
>  	platform_driver_unregister(&dcdbas_driver);
>  }
>  
--
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