Re: [PATCH v4 4/4] dmaengine: wait for RCU readers before releasing dma_device

On Tue, 2026-08-18 at 10:21 -0600, Logan Gunthorpe wrote:
> 
> On 2026-08-17 21:43, Shivank Garg wrote:
> > diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> > index d075051dd187..604c9af19936 100644
> > --- a/drivers/dma/dmaengine.c
> > +++ b/drivers/dma/dmaengine.c
> > @@ -429,6 +429,12 @@ static void dma_device_release(struct kref *ref)
> >  	list_del_rcu(&device->global_node);
> >  	dma_channel_rebalance();
> >  
> > +	/*
> > +	 * Wait for RCU readers (e.g. dma_issue_pending_all()) that may still
> > +	 * be traversing dma_device_list before the device is freed.
> > +	 */
> > +	synchronize_rcu();
> > +
> >  	if (device->device_release)
> >  		device->device_release(device);
> >  }
> > 
> 
> A couple minor points on this:
> 
> 1. I think the comment, as is, isn't useful. It's pretty clear the
> synchronize_rcu() call is paired with the list_del_rcu() call above it.
> 

Sure, I'll drop it.

> 2. The new synchronize_rcu() call will delay for a grace period with the
> dma_list_mutex lock held. Is that okay? It might be, but if so, it could
> use a note in the commit message.
> 

yeah, I believe it is okay as the added latency is confined to only
teardown path. I'll add note.

> Besides that, these are minor points and the patch does fix a real issue so:
> 
> Reviewed-by: Logan Gunthorpe <[email protected]>
> 
> 

Thanks for the review

Best regards,
Shivank