Merge: tracing: Ensure visibility when inserting an element into tracing_map

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/4659

JIRA: https://issues.redhat.com/browse/RHEL-30459
CVE: CVE-2024-26645

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

Approved-by: Waiman Long <longman@redhat.com>
Approved-by: John B. Wyatt IV <jwyatt@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Lucas Zampieri <lzampier@redhat.com>

Author: zampierilucas

kernel/trace/tracing_map.c

@@ -574,7 +574,12 @@ __tracing_map_insert(struct tracing_map *map, void *key, bool lookup_only)
 				}
 
 				memcpy(elt->key, key, map->key_size);
-				entry->val = elt;
+				/*
+				 * Ensure the initialization is visible and
+				 * publish the elt.
+				 */
+				smp_wmb();
+				WRITE_ONCE(entry->val, elt);
 				atomic64_inc(&map->hits);
 
 				return entry->val;