linux-kernel - Re: [PATCH] [FIX] dmaengine: virt-dma: Free descriptor after callback

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Date:	Fri, 18 Apr 2014 11:34:50 -0500
From:	Joel Fernandes <joelf@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	<dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-omap@...r.kernel.org>,
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH] [FIX] dmaengine: virt-dma: Free descriptor after callback

On 04/18/2014 03:50 AM, Russell King - ARM Linux wrote:
> On Thu, Apr 17, 2014 at 07:56:50PM -0500, Joel Fernandes wrote:
>> Free the vd (virt descriptor) after the callback is called.  In EDMA driver
>> atleast which uses virt-dma, we make use of the desc during the callback and if
>> its dangerously freed before the callback is called. I also noticed this in
>> omap-dma dmaengine driver.
> 
> You've missed the vital bit of information: why do you make use of the
> descriptor afterwards?  You shouldn't.  omap-dma doesn't either.
> 
> Once clients submit their request to DMA engine, they must not hold any
> kind of reference to the descriptor other than the cookie.
> 

Sorry, I confused edma/omap-dma callbacks for virt dma callbacks.

Anyway, I think there is still a chance in edma that we refer to the
echan->edesc pointer later on after virt-dma calls the free (in
edma_execute), so I'll just NULL that out to be safe and submit a patch.
Thanks.

regards,
  -Joel
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