Re: [Outreachy kernel] [PATCH v2 1/7] Staging: kpc2000: kpc_dma: Remove comparison to NULL.

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 25 Mar 2020 10:26:36 -0400
Sam Muhammed <jane.pnx9@gmail.com> wrote:

> Comparison to NULL been used across the driver,
> remove them and use (!var) instead.
> 
> Checkpatch.pl: CHECK:
> Comparison to NULL could be written "!desc"... etc
> 
> Signed-off-by: Sam Muhammed <jane.pnx9@gmail.com>
> ---
> Changes in v2:
> - None.
> 
>  drivers/staging/kpc2000/kpc_dma/dma.c            |  2 +-
>  drivers/staging/kpc2000/kpc_dma/fileops.c        | 12 ++++++------
>  drivers/staging/kpc2000/kpc_dma/kpc_dma_driver.h |  4 ++--
>  3 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/staging/kpc2000/kpc_dma/dma.c b/drivers/staging/kpc2000/kpc_dma/dma.c
> index 51a4dd534a0d..4bfbc717bc07 100644
> --- a/drivers/staging/kpc2000/kpc_dma/dma.c
> +++ b/drivers/staging/kpc2000/kpc_dma/dma.c
> @@ -236,7 +236,7 @@ int  count_descriptors_available(struct kpc_dma_device *eng)
>  	struct kpc_dma_descriptor *cur = eng->desc_next;
> 
>  	while (cur != eng->desc_completed) {
> -		BUG_ON(cur == NULL);
> +		BUG_ON(!cur);
>  		count++;
>  		cur = cur->Next;
>  	}
> diff --git a/drivers/staging/kpc2000/kpc_dma/fileops.c b/drivers/staging/kpc2000/kpc_dma/fileops.c
> index 40525540dde6..5eb6c5f24feb 100644
> --- a/drivers/staging/kpc2000/kpc_dma/fileops.c
> +++ b/drivers/staging/kpc2000/kpc_dma/fileops.c
> @@ -124,7 +124,7 @@ static int kpc_dma_transfer(struct dev_private_data *priv,
>  		pcnt = count_parts_for_sge(sg);
>  		for (p = 0 ; p < pcnt ; p++) {
>  			// Fill out the descriptor
> -			BUG_ON(desc == NULL);
> +			BUG_ON(!desc);
>  			clear_desc(desc);
>  			if (p != pcnt-1) {
>  				desc->DescByteCount = 0x80000;
> @@ -203,11 +203,11 @@ void  transfer_complete_cb(struct aio_cb_data *acd, size_t xfr_count, u32 flags)
>  {
>  	unsigned int i;
> 
> -	BUG_ON(acd == NULL);
> -	BUG_ON(acd->user_pages == NULL);
> -	BUG_ON(acd->sgt.sgl == NULL);
> -	BUG_ON(acd->ldev == NULL);
> -	BUG_ON(acd->ldev->pldev == NULL);
> +	BUG_ON(!acd);
> +	BUG_ON(!acd->user_pages);
> +	BUG_ON(!acd->sgt.sgl);
> +	BUG_ON(!acd->ldev);
> +	BUG_ON(!acd->ldev->pldev);

I've seen some tool reporting this (perhaps Coccinelle?): with
x == NULL, BUG_ON(!x) causes a kernel panic just like dereferencing x.
So the first statement in e.g.:

	BUG_ON(!acd);
	BUG_ON(!acd->user_pages);

is redundant. This change wouldn't be related to this patch, though.

-- 
Stefano