linux-kernel - Re: [PATCH v2 4/4] staging: kpc2000: kpc_dma: Remove additional goto statements

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Message-ID: <20200630094604.GK2571@kadam>
Date:   Tue, 30 Jun 2020 12:46:05 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     jane.pnx9@...il.com, ldufour@...ux.ibm.com,
        gregkh@...uxfoundation.org, harshjain32@...il.com,
        pakki001@....edu, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>,
        Bharath Vedartham <linux.bhar@...il.com>
Subject: Re: [PATCH v2 4/4] staging: kpc2000: kpc_dma: Remove additional goto
 statements

On Tue, Jun 30, 2020 at 01:22:19PM +0530, Souptick Joarder wrote:
> As 3 goto level referring to same common code, those can be
> accomodated with a single goto level and renameing it to
> unpin_pages. Set the -ERRNO when returning partial mapped
> pages in more appropriate place.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Bharath Vedartham <linux.bhar@...il.com>
> Cc: Dan Carpenter <dan.carpenter@...cle.com>
> ---
>  drivers/staging/kpc2000/kpc_dma/fileops.c | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/staging/kpc2000/kpc_dma/fileops.c b/drivers/staging/kpc2000/kpc_dma/fileops.c
> index 8cd20ad..d21a4fd 100644
> --- a/drivers/staging/kpc2000/kpc_dma/fileops.c
> +++ b/drivers/staging/kpc2000/kpc_dma/fileops.c
> @@ -35,7 +35,7 @@ static int kpc_dma_transfer(struct dev_private_data *priv,
>  			    unsigned long iov_base, size_t iov_len)
>  {
>  	unsigned int i = 0;
> -	int rv = 0;
> +	int rv = 0, nr_pages = 0;
>  	struct kpc_dma_device *ldev;
>  	struct aio_cb_data *acd;
>  	DECLARE_COMPLETION_ONSTACK(done);
> @@ -79,22 +79,27 @@ static int kpc_dma_transfer(struct dev_private_data *priv,
>  	rv = pin_user_pages(iov_base, acd->page_count, FOLL_TOUCH | FOLL_WRITE, acd->user_pages, NULL);
>  	mmap_read_unlock(current->mm);        /*  release the semaphore */
>  	if (rv != acd->page_count) {
> +		nr_pages = rv;
> +		if (rv > 0)
> +			rv = -EFAULT;
> +
>  		dev_err(&priv->ldev->pldev->dev, "Couldn't pin_user_pages (%d)\n", rv);
> -		goto err_get_user_pages;
> +		goto unpin_pages;
>  	}
> +	nr_pages = acd->page_count;
>  
>  	// Allocate and setup the sg_table (scatterlist entries)
>  	rv = sg_alloc_table_from_pages(&acd->sgt, acd->user_pages, acd->page_count, iov_base & (PAGE_SIZE - 1), iov_len, GFP_KERNEL);
>  	if (rv) {
>  		dev_err(&priv->ldev->pldev->dev, "Couldn't alloc sg_table (%d)\n", rv);
> -		goto err_alloc_sg_table;
> +		goto unpin_pages;
>  	}
>  
>  	// Setup the DMA mapping for all the sg entries
>  	acd->mapped_entry_count = dma_map_sg(&ldev->pldev->dev, acd->sgt.sgl, acd->sgt.nents, ldev->dir);
>  	if (acd->mapped_entry_count <= 0) {
>  		dev_err(&priv->ldev->pldev->dev, "Couldn't dma_map_sg (%d)\n", acd->mapped_entry_count);
> -		goto err_dma_map_sg;
> +		goto unpin_pages;

This wasn't introduced by your patch but the most recent successful
allocation is sg_alloc_table_from_pages() so this should be goto
free_table:

free_table:
	sg_free_table(&acd->sgt);
unpin_pages:
	if (nr_pages > 0)
		unpin_user_pages(acd->user_pages, nr_pages);

Always just keep track of the most recent allocation and check that the
"goto free_foo" matches what you would expect to release the most
recent thing.

>  	}
>  
>  	// Calculate how many descriptors are actually needed for this transfer.
> @@ -187,15 +192,10 @@ static int kpc_dma_transfer(struct dev_private_data *priv,
>  	unlock_engine(ldev);
>  	dma_unmap_sg(&ldev->pldev->dev, acd->sgt.sgl, acd->sgt.nents, ldev->dir);
>  	sg_free_table(&acd->sgt);
        ^^^^^^^^^^^^^^^^^^^^^^^^

> - err_dma_map_sg:
> - err_alloc_sg_table:
> -	unpin_user_pages(acd->user_pages, acd->page_count);
>  
> - err_get_user_pages:
> -	if (rv > 0) {
> -		unpin_user_pages(acd->user_pages, rv);
> -		rv = -EFAULT;
> -	}
> + unpin_pages:
> +	if (nr_pages > 0)
> +		unpin_user_pages(acd->user_pages, nr_pages);
>  	kfree(acd->user_pages);
>   err_alloc_userpages:
>  	kfree(acd);

regards,
dan carpenter