Re: [PATCH v3 1/3] cxl/region: Fix a race condition in memory hotplug notifier

[fan <nifan.cxl@gmail.com>]

On Tue, Jun 18, 2024 at 04:46:37PM +0800, Huang Ying wrote:
> In the memory hotplug notifier function of the CXL region,
> cxl_region_perf_attrs_callback(), the node ID is obtained by checking
> the host address range of the region. However, the address range
> information is not available when the region is registered in
> devm_cxl_add_region(). Additionally, this information may be removed
> or added under the protection of cxl_region_rwsem during runtime. If
> the memory notifier is called for nodes other than that backed by the
> region, a race condition may occur, potentially leading to a NULL
> dereference or an invalid address range.
> 
> The race condition is addressed by checking the availability of the
> address range information under the protection of cxl_region_rwsem. To
> enhance code readability and use guard(), the relevant code has been
> moved into a newly added function: cxl_region_nid().
> 
> Fixes: 067353a46d8c ("cxl/region: Add memory hotplug notifier for cxl region")
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Alison Schofield <alison.schofield@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Bharata B Rao <bharata@amd.com>
> Cc: Alistair Popple <apopple@nvidia.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> ---

Reviewed-by: Fan Ni <fan.ni@samsung.com>

>  drivers/cxl/core/region.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 3c2b6144be23..51aeef2c012c 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -2304,14 +2304,25 @@ static bool cxl_region_update_coordinates(struct cxl_region *cxlr, int nid)
>  	return true;
>  }
>  
> +static int cxl_region_nid(struct cxl_region *cxlr)
> +{
> +	struct cxl_region_params *p = &cxlr->params;
> +	struct cxl_endpoint_decoder *cxled;
> +	struct cxl_decoder *cxld;
> +
> +	guard(rwsem_read)(&cxl_region_rwsem);
> +	cxled = p->targets[0];
> +	if (!cxled)
> +		return NUMA_NO_NODE;
> +	cxld = &cxled->cxld;
> +	return phys_to_target_node(cxld->hpa_range.start);
> +}
> +
>  static int cxl_region_perf_attrs_callback(struct notifier_block *nb,
>  					  unsigned long action, void *arg)
>  {
>  	struct cxl_region *cxlr = container_of(nb, struct cxl_region,
>  					       memory_notifier);
> -	struct cxl_region_params *p = &cxlr->params;
> -	struct cxl_endpoint_decoder *cxled = p->targets[0];
> -	struct cxl_decoder *cxld = &cxled->cxld;
>  	struct memory_notify *mnb = arg;
>  	int nid = mnb->status_change_nid;
>  	int region_nid;
> @@ -2319,7 +2330,7 @@ static int cxl_region_perf_attrs_callback(struct notifier_block *nb,
>  	if (nid == NUMA_NO_NODE || action != MEM_ONLINE)
>  		return NOTIFY_DONE;
>  
> -	region_nid = phys_to_target_node(cxld->hpa_range.start);
> +	region_nid = cxl_region_nid(cxlr);
>  	if (nid != region_nid)
>  		return NOTIFY_DONE;
>  
> -- 
> 2.39.2
>