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Subject[patch] lockdep: improve verbose messages
Subject: [patch] lockdep: improve verbose messages
From: Ingo Molnar <mingo@elte.hu>

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>
---
kernel/lockdep.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux/kernel/lockdep.c
===================================================================
--- linux.orig/kernel/lockdep.c
+++ linux/kernel/lockdep.c
@@ -1266,7 +1266,7 @@ 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;
@@ -1288,9 +1288,13 @@ 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:
@@ -2140,7 +2144,7 @@ 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:
*
-
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