cxl/region: Fix a race condition in memory hotplug notifier

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: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://patch.msgid.link/20240618084639.1419629-2-ying.huang@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 3c2b6144be23cd1a6af9988f1e77b51fd4d421a5..51aeef2c012cfb698031109c86f085292ac89e3b 100644 (file)
--- 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;