Re: [PATCH] dmaengine: cppi41: Fix oops in cppi41_runtime_resume

[Grygorii Strashko <grygorii.strashko-l0cyMroinI0@public.gmane.org>]

On 01/12/2017 04:19 PM, Tony Lindgren wrote:
> * Grygorii Strashko <grygorii.strashko-l0cyMroinI0@public.gmane.org> [170112 13:54]:
>> On 01/12/2017 03:30 PM, Tony Lindgren wrote:
>>
>> Sry, but even if it looks better it might still race with PM runtime :(
>>
>>> -	if (likely(pm_runtime_active(cdd->ddev.dev)))
>>> +	if (likely(atomic_read(&cdd->active)))
>>>  		push_desc_queue(c);
>>>  	else
>>
>>
>> - CPU is here (-EINPROGRESS and active == 0) and then preempted 
>> - PM runtime will finish cppi41_runtime_resume and clean-up pending descs
>> - CPU return here and adds desc to the pending queue
>> - oops
>>
>> Am I wrong?
> 
> We had cppi41_dma_issue_pending() getting called from atomic contex and
> cppi41_runtime_resume() getting preempted where cppi41_dma_issue_pending()
> would add to the queue.

Again, I can be mistaken but cppi41_configure_channel() seems not atomic.
cppi41_configure_channel()->dma_async_issue_pending()
+ documentation says "This function can be called in an interrupt context"

And definitely it will be preemptive on RT :(

> 
> If what you're saying can happen in some cases, then we again see the
> WARN_ON(!list_empty(&cdd->pending)) in cppi41_runtime_suspend(). At least
> so far I have no longer been able to make happen today.

-- 
regards,
-grygorii
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