Re: [PATCH 1/4] dmaengine: Add transfer termination synchronization support
From: Lars-Peter Clausen
Date: Fri Oct 30 2015 - 10:16:24 EST
On 10/29/2015 10:59 PM, Andy Shevchenko wrote:
> On Tue, Oct 20, 2015 at 12:46 PM, Lars-Peter Clausen <lars@xxxxxxxxxx> 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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