[mono] Fix a race in gparam construction. (#83688)

vargaz · web-flow · commit 059898f8c0db · 2023-03-20T16:08:25.000-04:00
Re: #81123.
diff --git a/src/mono/mono/metadata/metadata.c b/src/mono/mono/metadata/metadata.c
@@ -3734,12 +3734,14 @@ publish_anon_gparam_fast (MonoImage *image, MonoGenericContainer *container, gin
 	if (!*cache) {
 		mono_image_lock (image);
 		if (!*cache) {
-			*cache = (MonoGenericParam*)mono_image_alloc0 (image, sizeof (MonoGenericParam) * FAST_GPARAM_CACHE_SIZE);
+			MonoGenericParam *new_cache = (MonoGenericParam*)mono_image_alloc0 (image, sizeof (MonoGenericParam) * FAST_GPARAM_CACHE_SIZE);
 			for (guint16 i = 0; i < FAST_GPARAM_CACHE_SIZE; ++i) {
-				MonoGenericParam *param = &(*cache)[i];
+				MonoGenericParam *param = &new_cache[i];
 				param->owner = container;
 				param->num = i;
 			}
+			mono_memory_barrier ();
+			*cache = new_cache;
 		}
 		mono_image_unlock (image);
 	}

Original file line number	Diff line number	Diff line change
`@@ -3734,12 +3734,14 @@ publish_anon_gparam_fast (MonoImage image, MonoGenericContainer container, gin`
`3734`	`3734`	`if (!*cache) {`
`3735`	`3735`	`mono_image_lock (image);`
`3736`	`3736`	`if (!*cache) {`
`3737`		`- cache = (MonoGenericParam)mono_image_alloc0 (image, sizeof (MonoGenericParam) * FAST_GPARAM_CACHE_SIZE);`
	`3737`	`+ MonoGenericParam new_cache = (MonoGenericParam)mono_image_alloc0 (image, sizeof (MonoGenericParam) * FAST_GPARAM_CACHE_SIZE);`
`3738`	`3738`	`for (guint16 i = 0; i < FAST_GPARAM_CACHE_SIZE; ++i) {`
`3739`		`- MonoGenericParam param = &(cache)[i];`
	`3739`	`+ MonoGenericParam *param = &new_cache[i];`
`3740`	`3740`	`param->owner = container;`
`3741`	`3741`	`param->num = i;`
`3742`	`3742`	`}`
	`3743`	`+ mono_memory_barrier ();`
	`3744`	`+ *cache = new_cache;`
`3743`	`3745`	`}`
`3744`	`3746`	`mono_image_unlock (image);`
`3745`	`3747`	`}`