rcu: Give different levels of the rcu_node hierarchy distinct lockdep names

Previously, each level of the rcu_node hierarchy had the same
rather unimaginative name: "&rcu_node_class[i]".  This makes
lockdep diagnostics involving these lockdep classes less helpful
than would be nice. This patch fixes this by giving each level
of the rcu_node hierarchy a distinct name: "rcu_node_level_0",
"rcu_node_level_1", and so on. This version of the patch
includes improved diagnostics suggested by Josh Triplett and
Peter Zijlstra.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626498421830-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 1 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0a4c32879398..3b13d64b010b 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1811,11 +1811,17 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp)
  */
 static void __init rcu_init_one(struct rcu_state *rsp)
 {
+        static char *buf[] = { "rcu_node_level_0",
+                               "rcu_node_level_1",
+                               "rcu_node_level_2",
+                               "rcu_node_level_3" };  /* Match MAX_RCU_LVLS */
         int cpustride = 1;
         int i;
         int j;
         struct rcu_node *rnp;
 
+        BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
+
         /* Initialize the level-tracking arrays. */
 
         for (i = 1; i < NUM_RCU_LVLS; i++)
@@ -1829,7 +1835,8 @@ static void __init rcu_init_one(struct rcu_state *rsp)
                 rnp = rsp->level[i];
                 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
                         spin_lock_init(&rnp->lock);
-                        lockdep_set_class(&rnp->lock, &rcu_node_class[i]);
+                        lockdep_set_class_and_name(&rnp->lock,
+                                                   &rcu_node_class[i], buf[i]);
                         rnp->gpnum = 0;
                         rnp->qsmask = 0;
                         rnp->qsmaskinit = 0;