Re: [PATCH v2 1/2] dmaengine: cppi41: Fix list not empty warning on runtime suspend

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

Hi,

* Alexandre Bailon <abailon-rdvid1DuHRBWk0Htik3J/w@public.gmane.org> [170109 09:04]:
> Sometime, a transfer may not be queued due to a race between runtime pm
> and cppi41_dma_issue_pending().
> Sometime, cppi41_runtime_resume() may be interrupted right before to
> update device PM state to RESUMED.
> When it happens, if a new dma transfer is issued, because the device is not
> in active state, the descriptor will be added to the pendding list.
> But because the descriptors in the pendding list are only queued to cppi41
> on runtime resume, the descriptor will not be queued.
> On runtime suspend, the list is not empty, which is causing a warning.
> Queue the descriptor if the device is active or resuming.
> 
> Signed-off-by: Alexandre Bailon <abailon-rdvid1DuHRBWk0Htik3J/w@public.gmane.org>
> ---
>  drivers/dma/cppi41.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/cppi41.c b/drivers/dma/cppi41.c
> index d5ba43a..025fee4 100644
> --- a/drivers/dma/cppi41.c
> +++ b/drivers/dma/cppi41.c
> @@ -471,6 +471,8 @@ static void cppi41_dma_issue_pending(struct dma_chan *chan)
>  {
>  	struct cppi41_channel *c = to_cpp41_chan(chan);
>  	struct cppi41_dd *cdd = c->cdd;
> +	unsigned long flags;
> +	bool active;
>  	int error;
>  
>  	error = pm_runtime_get(cdd->ddev.dev);
> @@ -482,7 +484,21 @@ static void cppi41_dma_issue_pending(struct dma_chan *chan)
>  		return;
>  	}
>  
> -	if (likely(pm_runtime_active(cdd->ddev.dev)))
> +	active = pm_runtime_active(cdd->ddev.dev);
> +	if (!active) {
> +		/*
> +		 * Runtime resume may be interrupted before runtime_status
> +		 * has been updated. Test if device has resumed.
> +		 */
> +		if (error == -EINPROGRESS) {
> +			spin_lock_irqsave(&cdd->lock, flags);
> +			if (list_empty(&cdd->pending))
> +				active = true;
> +			spin_unlock_irqrestore(&cdd->lock, flags);
> +		}
> +	}
> +
> +	if (likely(active))
>  		push_desc_queue(c);
>  	else
>  		pending_desc(c);

What guarantees that the PM runtime state is really active few lines later?

A safer approach might be to check the queue for new entries by in
cppi41_runtime_resume() using "while (!list_empty())" instead of
list_for_each_entry(). That releases the spinlock between each entry
and rechecks the list.

And instead of doing WARN_ON(!list_empty(&cdd->pending)) it seems we
should run the queue also on cppi41_runtime_suspend()?

Regards,

Tony
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