linux-kernel - Re: [PATCH resend] dma: pl330: Fix handling of TERMINATE_ALL while processing completed descriptors

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Message-ID: <20130828055738.GB11414@intel.com>
Date:	Wed, 28 Aug 2013 11:27:38 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Dan Williams <djbw@...com>,
	Jassi Brar <jaswinder.singh@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH resend] dma: pl330: Fix handling of TERMINATE_ALL while
 processing completed descriptors

On Tue, Aug 27, 2013 at 08:34:05PM +0200, Lars-Peter Clausen wrote:
> The pl330 DMA driver is broken in regard to handling a terminate all request
> while it is processing the list of completed descriptors. This is most visible
> when calling dmaengine_terminate_all() from within the descriptors callback for
> cyclic transfers. In this case the TERMINATE_ALL transfer will clear the
> work_list and stop the transfer. But after all callbacks for all completed
> descriptors have been handled the descriptors will be re-enqueued into the (now
> empty) work_list. So the next time dma_async_issue_pending() is called for the
> channel these descriptors will be transferred again which will cause data
> corruption. Similar issues can occur if dmaengine_terminate_all() is not called
> from within the descriptor callback but runs on a different CPU at the same time
> as the completed descriptor list is processed.
> 
> This patch introduces a new per channel list which will hold the completed
> descriptors. While processing the list the channel's lock will be held to avoid
> racing against dmaengine_terminate_all(). The lock will be released when calling
> the descriptors callback though. Since the list of completed descriptors might
> be modified (e.g. by calling dmaengine_terminate_all() from the callback) we can
> not use the normal list iterator macros. Instead we'll need to check for each
> loop iteration again if there are still items in the list. The drivers
> TERMINATE_ALL implementation is updated to move descriptors from both the
> work_list as well the new completed_list back to the descriptor pool. This makes
> sure that none of the descripts finds its way back into the work list and also
> that we do not call any futher complete callbacks after
> dmaengine_terminate_all() has been called.

Applied, thanks

~Vinod
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