linux-kernel - Re: [PATCH] arm64/dma-mapping: Fix null-pointer check

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Message-ID: <20170612122903.GC24187@e104818-lin.cambridge.arm.com>
Date:   Mon, 12 Jun 2017 13:29:04 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Olav Haugan <ohaugan@...eaurora.org>
Cc:     will.deacon@....com, robin.murphy@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64/dma-mapping: Fix null-pointer check

On Sat, Jun 10, 2017 at 12:41:10PM -0700, Olav Haugan wrote:
> @@ -149,6 +140,11 @@ static void *__dma_alloc(struct device *dev, size_t size,
>  	bool coherent = is_device_dma_coherent(dev);
>  	pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, false);
>  
> +	if (!dev) {
> +		WARN_ONCE(1, "Use an actual device structure for DMA allocation\n");
> +		return NULL;
> +	}
> +
>  	size = PAGE_ALIGN(size);
>  
>  	if (!coherent && !gfpflags_allow_blocking(flags)) {
> @@ -192,8 +188,13 @@ static void __dma_free(struct device *dev, size_t size,
>  		       void *vaddr, dma_addr_t dma_handle,
>  		       unsigned long attrs)
>  {
> -	void *swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));
> +	void *swiotlb_addr;
>  
> +	if (!dev) {
> +		WARN_ONCE(1, "Use an actual device structure for DMA free\n");
> +		return;
> +	}
> +	swiotlb_addr = phys_to_virt(dma_to_phys(dev, dma_handle));

I don't think we need the checks anymore. With commit 1dccb598df54
("arm64: simplify dma_get_ops") __generic_dma_ops() returns
dummy_dma_ops when dev == NULL, so the above __dma_alloc/__dma_free
functions would not be called.

-- 
Catalin