linux-kernel - Re: [PATCH 1/4] dmaengine: Add transfer termination synchronization support

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Message-ID: <56337BAD.2060506@metafoo.de>
Date:	Fri, 30 Oct 2015 15:16:13 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
CC:	Vinod Koul <vinod.koul@...el.com>, Takashi Iwai <tiwai@...e.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Laurent Pinchart <renesas@...asonboard.com>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	Qiao Zhou <zhouqiao@...vell.com>,
	Shengjiu Wang <shengjiu.wang@...escale.com>,
	Matt Campbell <mcampbell@...tope.com>,
	Jonah Petri <jpetri@...tope.com>,
	dmaengine <dmaengine@...r.kernel.org>,
	alsa-devel@...a-project.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] dmaengine: Add transfer termination synchronization
 support

On 10/29/2015 10:59 PM, Andy Shevchenko wrote:
> On Tue, Oct 20, 2015 at 12:46 PM, Lars-Peter Clausen <lars@...afoo.de> wrote:
>> The DMAengine API has a long standing race condition that is inherent to
>> the API itself. Calling dmaengine_terminate_all() is supposed to stop and
>> abort any pending or active transfers that have previously been submitted.
>> Unfortunately it is possible that this operation races against a currently
>> running (or with some drivers also scheduled) completion callback.
> 
> []
> 
>> +/**
>> + * dmaengine_terminate_sync() - Terminate all active DMA transfers
>> + * @chan: The channel for which to terminate the transfers
>> + *
>> + * Calling this function will terminate all active and pending transfers
>> + * that have previously been submitted to the channel. It is similar to
>> + * dmaengine_terminate_async() but guarantees that the DMA transfer has actually
>> + * stopped and that all complete callbacks have finished running when the
>> + * function returns.
>> + *
>> + * This function must only be called from non-atomic context and must not be
>> + * called from within a complete callback of a descriptor submitted on the same
>> + * channel.
>> + */
>> +static inline int dmaengine_terminate_sync(struct dma_chan *chan)
>> +{
>> +       int ret;
> 
> Might be a good idea to add might_sleep(); here.

Sound like a good idea, thanks, I'll add it (in dmaengine_synchronize() though).

> 
>> +
>> +       ret = dmaengine_terminate_async(chan);
>> +       if (ret)
>> +               return ret;
>> +
>> +       dmaengine_synchronize(chan);
>> +
>> +       return 0;
>> +}
> 
> 

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