Re: [PATCH v4] mmc: block: Fix bug when removing RPMB chardev

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On 04/10/17 12:10, Linus Walleij wrote:
> I forgot to account for the fact that the device core holds a
> reference to a device added with device_initialize() that need
> to be released with a corresponding put_device() to reach a 0
> refcount at the end of the lifecycle.
> 
> This led to a NULL pointer reference when freeing the device
> when e.g. unbidning the host device in sysfs.
> 
> Fix this and use the device .release() callback to free the
> IDA and free:ing the memory used by the RPMB device.
> 
> Before this patch:
> 
> /sys/bus/amba/drivers/mmci-pl18x$ echo 80114000.sdi4_per2 > unbind
> [   29.797332] mmc3: card 0001 removed
> [   29.810791] Unable to handle kernel NULL pointer dereference at
>                virtual address 00000050
> [   29.818878] pgd = de70c000
> [   29.821624] [00000050] *pgd=1e70a831, *pte=00000000, *ppte=00000000
> [   29.827911] Internal error: Oops: 17 [#1] PREEMPT SMP ARM
> [   29.833282] Modules linked in:
> [   29.836334] CPU: 1 PID: 154 Comm: sh Not tainted
>                4.14.0-rc3-00039-g83318e309566-dirty #736
> [   29.844604] Hardware name: ST-Ericsson Ux5x0 platform (Device Tree Support)
> [   29.851562] task: de572700 task.stack: de742000
> [   29.856079] PC is at kernfs_find_ns+0x8/0x100
> [   29.860443] LR is at kernfs_find_and_get_ns+0x30/0x48
> 
> After this patch:
> 
> /sys/bus/amba/drivers/mmci-pl18x$ echo 80005000.sdi4_per2 > unbind
> [   20.623382] mmc3: card 0001 removed
> 
> Fixes: 0ab0c7c0e65a ("mmc: block: Convert RPMB to a character device")
> Reported-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>


Acked-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>


> ---
> ChangeLog v3->v4:
> - Also skip the lock now that we take it inside mmc_blk_get()/
>   mmc_blk_put()
> ChangeLog v2->v3:
> - Fix the block device reference counting: instead of manipulating
>   md->usage directly, call the proper refcounting functions
>   mmc_blk_get() and mmc_blk_put().
> ChangeLog v1->v2:
> - Drop the print from removing the RPMB partition
> - Refactor the error path of the RPMB to use refcounting
> - Drop the verbose comment on refcounts
> ---
>  drivers/mmc/core/block.c | 32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index c29dbcec7c61..ea80ff4cd7f9 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -2298,9 +2298,7 @@ static int mmc_rpmb_chrdev_open(struct inode *inode, struct file *filp)
>  
>  	get_device(&rpmb->dev);
>  	filp->private_data = rpmb;
> -	mutex_lock(&open_lock);
> -	rpmb->md->usage++;
> -	mutex_unlock(&open_lock);
> +	mmc_blk_get(rpmb->md->disk);
>  
>  	return nonseekable_open(inode, filp);
>  }
> @@ -2311,9 +2309,7 @@ static int mmc_rpmb_chrdev_release(struct inode *inode, struct file *filp)
>  						  struct mmc_rpmb_data, chrdev);
>  
>  	put_device(&rpmb->dev);
> -	mutex_lock(&open_lock);
> -	rpmb->md->usage--;
> -	mutex_unlock(&open_lock);
> +	mmc_blk_put(rpmb->md);
>  
>  	return 0;
>  }
> @@ -2329,6 +2325,13 @@ static const struct file_operations mmc_rpmb_fileops = {
>  #endif
>  };
>  
> +static void mmc_blk_rpmb_device_release(struct device *dev)
> +{
> +	struct mmc_rpmb_data *rpmb = dev_get_drvdata(dev);
> +
> +	ida_simple_remove(&mmc_rpmb_ida, rpmb->id);
> +	kfree(rpmb);
> +}
>  
>  static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
>  				   struct mmc_blk_data *md,
> @@ -2347,8 +2350,10 @@ static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
>  		return devidx;
>  
>  	rpmb = kzalloc(sizeof(*rpmb), GFP_KERNEL);
> -	if (!rpmb)
> +	if (!rpmb) {
> +		ida_simple_remove(&mmc_rpmb_ida, devidx);
>  		return -ENOMEM;
> +	}
>  
>  	snprintf(rpmb_name, sizeof(rpmb_name),
>  		 "mmcblk%u%s", card->host->index, subname ? subname : "");
> @@ -2359,6 +2364,7 @@ static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
>  	rpmb->dev.bus = &mmc_rpmb_bus_type;
>  	rpmb->dev.devt = MKDEV(MAJOR(mmc_rpmb_devt), rpmb->id);
>  	rpmb->dev.parent = &card->dev;
> +	rpmb->dev.release = mmc_blk_rpmb_device_release;
>  	device_initialize(&rpmb->dev);
>  	dev_set_drvdata(&rpmb->dev, rpmb);
>  	rpmb->md = md;
> @@ -2368,7 +2374,7 @@ static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
>  	ret = cdev_device_add(&rpmb->chrdev, &rpmb->dev);
>  	if (ret) {
>  		pr_err("%s: could not add character device\n", rpmb_name);
> -		goto out_remove_ida;
> +		goto out_put_device;
>  	}
>  
>  	list_add(&rpmb->node, &md->rpmbs);
> @@ -2383,18 +2389,16 @@ static int mmc_blk_alloc_rpmb_part(struct mmc_card *card,
>  
>  	return 0;
>  
> -out_remove_ida:
> -	ida_simple_remove(&mmc_rpmb_ida, rpmb->id);
> -	kfree(rpmb);
> +out_put_device:
> +	put_device(&rpmb->dev);
>  	return ret;
>  }
>  
>  static void mmc_blk_remove_rpmb_part(struct mmc_rpmb_data *rpmb)
> +
>  {
>  	cdev_device_del(&rpmb->chrdev, &rpmb->dev);
> -	device_del(&rpmb->dev);
> -	ida_simple_remove(&mmc_rpmb_ida, rpmb->id);
> -	kfree(rpmb);
> +	put_device(&rpmb->dev);
>  }
>  
>  /* MMC Physical partitions consist of two boot partitions and
> 

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