[SPARC64]: Fix MD property lifetime bugs.

Property values cannot be referenced outside of
mdesc_grab()/mdesc_release() pairs.  The only major
offender was the VIO bus layer, easily fixed.

Add some commentary to mdesc.h describing these rules.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 2 deletions

diff --git a/include/asm-sparc64/mdesc.h b/include/asm-sparc64/mdesc.h
index bbb0c0bed486..dc372df23fb3 100644
--- a/include/asm-sparc64/mdesc.h
+++ b/include/asm-sparc64/mdesc.h
@@ -23,8 +23,28 @@ extern u64 mdesc_node_by_name(struct mdesc_handle *handle,
              (__node) != MDESC_NODE_NULL; \
              __node = mdesc_node_by_name(__hdl, __node, __name))
 
+/* Access to property values returned from mdesc_get_property() are
+ * only valid inside of a mdesc_grab()/mdesc_release() sequence.
+ * Once mdesc_release() is called, the memory backed up by these
+ * pointers may reference freed up memory.
+ *
+ * Therefore callers must make copies of any property values
+ * they need.
+ *
+ * These same rules apply to mdesc_node_name().
+ */
 extern const void *mdesc_get_property(struct mdesc_handle *handle,
                                       u64 node, const char *name, int *lenp);
+extern const char *mdesc_node_name(struct mdesc_handle *hp, u64 node);
+
+/* MD arc iteration, the standard sequence is:
+ *
+ *      unsigned long arc;
+ *      mdesc_for_each_arc(arc, handle, node, MDESC_ARC_TYPE_{FWD,BACK}) {
+ *              unsigned long target = mdesc_arc_target(handle, arc);
+ *              ...
+ *      }
+ */
 
 #define MDESC_ARC_TYPE_FWD      "fwd"
 #define MDESC_ARC_TYPE_BACK     "back"
@@ -38,8 +58,6 @@ extern u64 mdesc_next_arc(struct mdesc_handle *handle, u64 from,
 
 extern u64 mdesc_arc_target(struct mdesc_handle *hp, u64 arc);
 
-extern const char *mdesc_node_name(struct mdesc_handle *hp, u64 node);
-
 extern void mdesc_update(void);
 
 extern void sun4v_mdesc_init(void);