linux-kernel - Re: [PATCH] arm64: Use and error-check DMA_ERROR

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Date:	Wed, 1 Oct 2014 14:52:48 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Will Deacon <will.deacon@....com>
Cc:	Sean Paul <seanpaul@...omium.org>,
	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ritesh.harjani@...il.com" <ritesh.harjani@...il.com>,
	"olof@...om.net" <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: Use and error-check DMA_ERROR_CODE

On Wed, Oct 01, 2014 at 11:13:23AM +0100, Will Deacon wrote:
> Hi Sean,
> 
> On Tue, Sep 30, 2014 at 09:15:21PM +0100, Sean Paul wrote:
> > +
> > +	if (dma_handle != DMA_ERROR_CODE)
> > +		__dma_free_coherent(dev, size, swiotlb_addr, dma_handle, attrs);
> 
> Is it legal to try and free a DMA buffer after a failed allocation? If so, I
> think we need something similar for arch/arm/.

No.

	void
	dma_free_coherent(struct device *dev, size_t size, void *cpu_addr,
	                           dma_addr_t dma_handle)

	Free a region of consistent memory you previously allocated.  dev,
	                                       ^^^^^^^^^^^^^^^^^^^^^
This implies that the allocation was successful.

	size and dma_handle must all be the same as those passed into
	dma_alloc_coherent().  cpu_addr must be the virtual address returned by
	                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you want this behaviour, the proper way to do it would be to check
for a NULL cpu_addr, just like kfree() etc.

	the dma_alloc_coherent().

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