linux-kernel - Re: [PATCH] dma-buf: Remove unnecessary kmalloc() cast

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Date: Mon, 1 Jul 2024 23:26:34 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Thorsten Blum <thorsten.blum@...lux.com>
Cc: jack@...e.cz, surenb@...gle.com, linux-kernel@...r.kernel.org, Christoph
 Hellwig <hch@....de>
Subject: Re: [PATCH] dma-buf: Remove unnecessary kmalloc() cast

On Sun, 30 Jun 2024 03:12:16 +0200 Thorsten Blum <thorsten.blum@...lux.com> wrote:

> Casting the return value of kmalloc() is unnecessary and can be
> removed. Remove it and fix the following Coccinelle/coccicheck warning
> reported by alloc_cast.cocci:
> 
>   WARNING: casting value returned by memory allocation function to (struct dma_fence_chain *) is useless.
> 
> Compile-tested only.
> 
> ...
>
> --- a/include/linux/dma-fence-chain.h
> +++ b/include/linux/dma-fence-chain.h
> @@ -87,7 +87,7 @@ dma_fence_chain_contained(struct dma_fence *fence)
>   * Returns a new struct dma_fence_chain object or NULL on failure.
>   */
>  #define dma_fence_chain_alloc()	\
> -		((struct dma_fence_chain *)kmalloc(sizeof(struct dma_fence_chain), GFP_KERNEL))
> +		kmalloc(sizeof(struct dma_fence_chain), GFP_KERNEL)
>  
>  /**
>   * dma_fence_chain_free

No, I do think the cast is useful:

	struct page *page = dma_fence_chain_alloc();

will presently generate a warning.  We want this.  Your change will
remove that useful warning.


Unrelatedly: there is no earthly reason why this is implemented as a
macro.  A static inline function would be so much better.  Why do we
keep doing this.