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

[Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org>]

* Grygorii Strashko <grygorii.strashko-l0cyMroinI0@public.gmane.org> [170112 14:53]:
> 
> 
> 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 :(

Hmm OK. So are you thinking we should add a spinlock around the
test in cppi41_dma_issue_pending() and when modifying cdd->active?

Something like:

spin_lock_irqsave(&cdd->lock, flags);
if (likely(cdd->active))
	push_desc_queue(c);
else
	list_add_tail(&c->node, &cdd->pending);
spin_unlock_irqrestore(&cdd->lock, flags);

Or do you have something better in mind?

Regards,

Tony
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