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

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Message-ID: <CAHp75Vey9zQMCWB63BDsOqEGKQh3SvANWCbH1har-vmXoAquXQ@mail.gmail.com>
Date:	Thu, 29 Oct 2015 23:59:40 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
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 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.

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


-- 
With Best Regards,
Andy Shevchenko
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