linux-kernel - Re: [PATCH v2] dmaengine: edma: Implement device

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Date:	Thu, 11 Feb 2016 10:41:45 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Peter Ujfalusi <peter.ujfalusi@...com>, vinod.koul@...el.com
Cc:	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, nsekhar@...com,
	linux-omap@...r.kernel.org
Subject: Re: [PATCH v2] dmaengine: edma: Implement device_synchronize callback

On 02/11/2016 10:08 AM, Peter Ujfalusi wrote:
> We need the callback to support the dmaengine_terminate_sync().
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>

Looks good, but I noticed a slight race condition in
edma_completion_handler(). You need to fetch echan->desc while holding the
vchan.lock. Otherwise this can race against terminate_all() and the callback
might get scheduled even though terminate_all() completed and then there is
a race where the synchronize() operation could be called before the callback
gets scheduled, which means it doesn't do its intended job. Highly unlikely
to happen, but theoretically possible.