[PATCH] lockdep: improve verbose messages

Make verbose lockdep messages (off by default) more informative by printing
out the hash chain key.  (this patch was what helped me catch the earlier
lockdep hash-collision bug)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 5d69c7d7407e..5ba2825bd46a 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -1264,7 +1264,7 @@ out_unlock_set:
  * add it and return 0 - in this case the new dependency chain is
  * validated. If the key is already hashed, return 1.
  */
-static inline int lookup_chain_cache(u64 chain_key)
+static inline int lookup_chain_cache(u64 chain_key, struct lock_class *class)
 {
         struct list_head *hash_head = chainhashentry(chain_key);
         struct lock_chain *chain;
@@ -1286,9 +1286,13 @@ cache_hit:
                         __raw_spin_lock(&hash_lock);
                         return 1;
 #endif
+                        if (very_verbose(class))
+                                printk("\nhash chain already cached, key: %016Lx tail class: [%p] %s\n", chain_key, class->key, class->name);
                         return 0;
                 }
         }
+        if (very_verbose(class))
+                printk("\nnew hash chain, key: %016Lx tail class: [%p] %s\n", chain_key, class->key, class->name);
         /*
          * Allocate a new chain entry from the static array, and add
          * it to the hash:
@@ -2139,7 +2143,7 @@ out_calc_hash:
          * (If lookup_chain_cache() returns with 1 it acquires
          * hash_lock for us)
          */
-        if (!trylock && (check == 2) && lookup_chain_cache(chain_key)) {
+        if (!trylock && (check == 2) && lookup_chain_cache(chain_key, class)) {
                 /*
                  * Check whether last held lock:
                  *