Re: [alsa-devel] [PATCH 1/4] dmaengine: Add transfer termination synchronization support

On Tue, Oct 20, 2015 at 12:46 PM, Lars-Peter Clausen lars@metafoo.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;
  

+}