Re: [PATCH v3 21/25] dax/region: Create resources on sparse DAX regions

[Ira Weiny <ira.weiny@intel.com>]

Jonathan Cameron wrote:
> On Fri, 16 Aug 2024 09:44:29 -0500
> ira.weiny@intel.com wrote:
> 
> > From: Navneet Singh <navneet.singh@intel.com>
> > 

[snip]

> > diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> > index d7d526a51e2b..103b0bec3a4a 100644
> > --- a/drivers/cxl/core/extent.c
> > +++ b/drivers/cxl/core/extent.c
> > @@ -271,20 +271,67 @@ static void calc_hpa_range(struct cxl_endpoint_decoder *cxled,
> >  	hpa_range->end = hpa_range->start + range_len(dpa_range) - 1;
> >  }
> >  
> > +static int cxlr_notify_extent(struct cxl_region *cxlr, enum dc_event event,
> > +			      struct region_extent *region_extent)
> > +{
> > +	struct cxl_dax_region *cxlr_dax;
> > +	struct device *dev;
> > +	int rc = 0;
> > +
> > +	cxlr_dax = cxlr->cxlr_dax;
> > +	dev = &cxlr_dax->dev;
> > +	dev_dbg(dev, "Trying notify: type %d HPA %par\n",
> > +		event, &region_extent->hpa_range);
> > +
> > +	/*
> > +	 * NOTE the lack of a driver indicates a notification has failed.  No
> > +	 * user space coordiantion was possible.
> > +	 */
> > +	device_lock(dev);
> 
> I'd use guard() for this as then can just return the notify result
> and drop local variable rc

Yep Dave already mentioned this and it is done.

> 
> 
> > +	if (dev->driver) {
> > +		struct cxl_driver *driver = to_cxl_drv(dev->driver);
> > +		struct cxl_notify_data notify_data = (struct cxl_notify_data) {
> > +			.event = event,
> > +			.region_extent = region_extent,
> > +		};
> > +
> > +		if (driver->notify) {
> > +			dev_dbg(dev, "Notify: type %d HPA %par\n",
> > +				event, &region_extent->hpa_range);
> > +			rc = driver->notify(dev, &notify_data);
> > +		}
> > +	}
> > +	device_unlock(dev);
> > +	return rc;
> > +}
> >
> > @@ -338,8 +390,20 @@ static int cxlr_add_extent(struct cxl_dax_region *cxlr_dax,
> >  		return rc;
> >  	}
> >  
> > -	/* device model handles freeing region_extent */
> > -	return online_region_extent(region_extent);
> > +	rc = online_region_extent(region_extent);
> > +	/* device model handled freeing region_extent */
> > +	if (rc)
> > +		return rc;
> > +
> > +	rc = cxlr_notify_extent(cxlr_dax->cxlr, DCD_ADD_CAPACITY, region_extent);
> > +	/*
> > +	 * The region device was breifly live but DAX layer ensures it was not
> 
> briefly

Fixed Thanks

> 
> > +	 * used
> > +	 */
> > +	if (rc)
> > +		region_rm_extent(region_extent);	
> > +
> > +	return rc;
> >  }
> 
> > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> > index 975860371d9f..f14b0cfa7edd 100644
> > --- a/drivers/dax/bus.c
> > +++ b/drivers/dax/bus.c
> 
> > +EXPORT_SYMBOL_GPL(dax_region_add_resource);
> > +
> > +int dax_region_rm_resource(struct dax_region *dax_region,
> > +			   struct device *dev)
> > +{
> > +	struct dax_resource *dax_resource;
> > +
> > +	guard(rwsem_write)(&dax_region_rwsem);
> > +
> > +	dax_resource = dev_get_drvdata(dev);
> > +	if (!dax_resource)
> > +		return 0;
> > +
> > +	if (dax_resource->use_cnt)
> > +		return -EBUSY;
> > +
> > +	/* avoid races with users trying to use the extent */
> 
> Not obvious to me from local code, why does releasing the resource
> here avoid a race?  Perhaps the comment needs expanding.

We are under the dax_region_rwsem here.  So that avoids the users from seeing
the extent while the lower level code is going to remove it.

How about?

        /*
         * release the resource under dax_region_rwsem to avoid races with
         * users trying to use the extent
         */

> 
> > +	__dax_release_resource(dax_resource);
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(dax_region_rm_resource);
> > +
> 
> 
> > +static ssize_t dev_dax_resize_sparse(struct dax_region *dax_region,
> > +				     struct dev_dax *dev_dax,
> > +				     resource_size_t to_alloc)
> > +{
> > +	struct dax_resource *dax_resource;
> > +	resource_size_t available_size;
> > +	struct device *extent_dev;
> > +	ssize_t alloc;
> > +
> > +	extent_dev = device_find_child(dax_region->dev, dax_region,
> > +				       find_free_extent);
> 
> There is a __free for put device and it will tidy this up a tiny bit.

And fix the bug...  :-/  Thanks.

> 
> > +	if (!extent_dev)
> > +		return 0;
> > +
> > +	dax_resource = dev_get_drvdata(extent_dev);
> > +	if (!dax_resource)
> > +		return 0;
> > +
> > +	available_size = dax_avail_size(dax_resource->res);
> > +	to_alloc = min(available_size, to_alloc);
> I'd put those two inline and skip the local variables unless
> they have more use in later patches.

Nope just made the line shorter and I tend to not embed calls like that but it
is fine your way too.  I'll change it.

> 
> 	alloc = __dev_dax_resize(dax_resources->res, dev_dax,
> 				 min(dax_avail_size(dax_resources->res), to_alloc),
> 				 dax_resource);
> 	
> 				
> > +	alloc = __dev_dax_resize(dax_resource->res, dev_dax, to_alloc, dax_resource);
> > +	if (alloc > 0)
> > +		dax_resource->use_cnt++;
> > +	put_device(extent_dev);
> > +	return alloc;
> > +}
> > +
> 
> > @@ -1494,8 +1679,14 @@ static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data)
> >  	device_initialize(dev);
> >  	dev_set_name(dev, "dax%d.%d", dax_region->id, dev_dax->id);
> >  
> > +	if (is_sparse(dax_region) && data->size) {
> > +		dev_err(parent, "Sparse DAX region devices are created initially with 0 size");
> must be created initially with 0 size.
> 
> Otherwise this error message says that they are, so why is it an error?

Indeed!

> 
> > +		rc = -EINVAL;
> > +		goto err_id;
> > +	}
> > +
> >  	rc = alloc_dev_dax_range(&dax_region->res, dev_dax, dax_region->res.start,
> > -				 data->size);
> > +				 data->size, NULL);
> >  	if (rc)
> >  		goto err_range;
> >  
> 
> > diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
> > index 367e86b1c22a..bf3b82b0120d 100644
> > --- a/drivers/dax/cxl.c
> > +++ b/drivers/dax/cxl.c
> > @@ -5,6 +5,60 @@
> 
> ...
> 
> > +static int cxl_dax_region_notify(struct device *dev,
> > +				 struct cxl_notify_data *notify_data)
> > +{
> > +	struct cxl_dax_region *cxlr_dax = to_cxl_dax_region(dev);
> > +	struct dax_region *dax_region = dev_get_drvdata(dev);
> > +	struct region_extent *region_extent = notify_data->region_extent;
> > +
> > +	switch (notify_data->event) {
> > +	case DCD_ADD_CAPACITY:
> > +		return __cxl_dax_add_resource(dax_region, region_extent);
> > +	case DCD_RELEASE_CAPACITY:
> > +		return dax_region_rm_resource(dax_region, &region_extent->dev);
> > +	case DCD_FORCED_CAPACITY_RELEASE:
> > +	default:
> > +		dev_err(&cxlr_dax->dev, "Unknown DC event %d\n",
> > +			notify_data->event);
> > +		break;
> Might as well return here and not below.
> Makes it really really obvious this is the error path and currently the only
> one that hits the return statement.
> > +	}

ok

> > +
> > +	return -ENXIO;
> > +}
> 
> >  static int cxl_dax_region_probe(struct device *dev)
> >  {
> > @@ -24,14 +78,16 @@ static int cxl_dax_region_probe(struct device *dev)
> >  		flags |= IORESOURCE_DAX_SPARSE_CAP;
> >  
> >  	dax_region = alloc_dax_region(dev, cxlr->id, &cxlr_dax->hpa_range, nid,
> > -				      PMD_SIZE, flags);
> > +				      PMD_SIZE, flags, &sparse_ops);
> >  	if (!dax_region)
> >  		return -ENOMEM;
> >  
> > -	if (cxlr->mode == CXL_REGION_DC)
> > +	if (cxlr->mode == CXL_REGION_DC) {
> > +		device_for_each_child(&cxlr_dax->dev, dax_region,
> > +				      cxl_dax_add_resource);
> >  		/* Add empty seed dax device */
> >  		dev_size = 0;
> > -	else
> > +	} else
> 
> Coding style says that you need brackets for all branches if
> one needs them (as multiline).  Just above:
> https://www.kernel.org/doc/html/v4.10/process/coding-style.html#spaces
> 

Yep missed it.  thanks for the review!
Ira

[snip]