Re: [PATCH rc 2/2] iommufd/fault: Use a separate spinlock to protect fault->deliver list

[Nicolin Chen <nicolinc@nvidia.com>]

On Wed, Jan 15, 2025 at 01:24:53PM +0800, Baolu Lu wrote:
> On 1/15/25 07:28, Nicolin Chen wrote:
> > @@ -445,12 +445,38 @@ struct iommufd_fault {
> >   	/* The lists of outstanding faults protected by below mutex. */
> 
> It's better to update above comment as well.
> 
> >   	struct mutex mutex;
> > +	spinlock_t lock; /* protects the deliver list */
> >   	struct list_head deliver;
> >   	struct xarray response;

Ack. I'll do:
-	/* The lists of outstanding faults protected by below mutex. */
-	struct mutex mutex;
+	spinlock_t lock; /* protects the deliver list */
 	struct list_head deliver;
+	struct mutex mutex; /* serializes response flows */
 	struct xarray response;

> >   	struct wait_queue_head wait_queue;
> >   };
> > +/* Extract the first node out of the fault->deliver list */
> > +static inline struct iopf_group *
> > +iommufd_fault_deliver_extract(struct iommufd_fault *fault)
> > +{
> > +	struct list_head *list = &fault->deliver;
> > +	struct iopf_group *group = NULL;
> > +
> > +	spin_lock(&fault->lock);
> > +	if (!list_empty(list)) {
> > +		group = list_first_entry(list, struct iopf_group, node);
> > +		list_del(&group->node);
> > +	}
> > +	spin_unlock(&fault->lock);
> > +	return group;
> > +}
> > +
> > +/* Restore a node back to the head in fault->deliver */
> > +static inline void iommufd_fault_deliver_restore(struct iommufd_fault *fault,
> > +						 struct iopf_group *group)
> > +{
> > +	spin_lock(&fault->lock);
> > +	list_add(&fault->deliver, &group->node);
> 
> This is not right. It should be
> 
> 	list_add(&group->node, &fault->deliver);
> 
> > +	spin_unlock(&fault->lock);
> > +}

Oh, right!

> Others look good to me. With above addressed,
> 
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

Thanks!
Nicolin