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LOCKDEP: fix mismatched lockdep_depth/curr_chain_hash

PATCH New Gregory Haskins 2 participants 2 messages Oct 5, 2007

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Gregory Haskins

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#0 lore raw

PATCH 1/1 LOCKDEP: fix mismatched lockdep_depth/curr_chain_hash

Doh! I guess there should be a rule about sending patches out after midnight ;)

The original patch I worked on was written before the code was moved to validate_chain(), so my previous posting didnt quite translate when I merged with git HEAD. Here is an updated patch. Sorry for the confusion.

Regards,
-Greg

---

 kernel/lockdep.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)
kernel/lockdep.c +5 -5
index 734da57..42ae4a5 100644
@@ -1521,7 +1521,7 @@ cache_hit:
 }
 
 static int validate_chain(struct task_struct *curr, struct lockdep_map *lock,
-	       	struct held_lock *hlock, int chain_head)
+	       	struct held_lock *hlock, int chain_head, u64 chain_key)
 {
 	/*
 	 * Trylock needs to maintain the stack of held locks, but it

@@ -1534,7 +1534,7 @@ static int validate_chain(struct task_struct *curr, struct lockdep_map *lock,
 	 * graph_lock for us)
 	 */
 	if (!hlock->trylock && (hlock->check == 2) &&
-			lookup_chain_cache(curr->curr_chain_key, hlock->class)) {
+			lookup_chain_cache(chain_key, hlock->class)) {
 		/*
 		 * Check whether last held lock:
 		 *

@@ -1576,7 +1576,7 @@ static int validate_chain(struct task_struct *curr, struct lockdep_map *lock,
 #else
 static inline int validate_chain(struct task_struct *curr,
 	       	struct lockdep_map *lock, struct held_lock *hlock,
-		int chain_head)
+		int chain_head, u64 chain_key)
 {
 	return 1;
 }

@@ -2450,11 +2450,11 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 		chain_head = 1;
 	}
 	chain_key = iterate_chain_key(chain_key, id);
-	curr->curr_chain_key = chain_key;
 
-	if (!validate_chain(curr, lock, hlock, chain_head))
+	if (!validate_chain(curr, lock, hlock, chain_head, chain_key))
 		return 0;
 
+	curr->curr_chain_key = chain_key;
 	curr->lockdep_depth++;
 	check_chain_key(curr);
 #ifdef CONFIG_DEBUG_LOCKDEP
#1 lore raw

PATCH 1/1 lockdep: fix mismatched lockdep_depth/curr_chain_hash

Ouch!

Thanks Gregory for finding this!

I'll send your initial patch to the stable team for .22.

---
Subject: lockdep: fix mismatched lockdep_depth/curr_chain_hash
From: Gregory Haskins <[email protected]>

It is possible for the current->curr_chain_key to become inconsistent with the current index if the chain fails to validate. The end result is that future lock_acquire() operations may inadvertently fail to find a hit in the cache resulting in a new node being added to the graph for every acquire.

[ peterz: this might explain some of the lockdep is so _slow_ complaints. ] [ mingo: this does not impact the correctness of validation, but may slow
down future operations significantly, if the chain gets very long. ]

Signed-off-by Gregory Haskins <[email protected]>
Signed-off-by Peter Zijlstra <[email protected]>
Signed-off-by Ingo Molnar <[email protected]>
---
 kernel/lockdep.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
kernel/lockdep.c +5 -5
Index: linux-2.6/kernel/lockdep.c
===================================================================
@@ -1521,7 +1521,7 @@ cache_hit:
 }
 
 static int validate_chain(struct task_struct *curr, struct lockdep_map *lock,
-	       	struct held_lock *hlock, int chain_head)
+	       	struct held_lock *hlock, int chain_head, u64 chain_key)
 {
 	/*
 	 * Trylock needs to maintain the stack of held locks, but it

@@ -1534,7 +1534,7 @@ static int validate_chain(struct task_st
 	 * graph_lock for us)
 	 */
 	if (!hlock->trylock && (hlock->check == 2) &&
-			lookup_chain_cache(curr->curr_chain_key, hlock->class)) {
+			lookup_chain_cache(chain_key, hlock->class)) {
 		/*
 		 * Check whether last held lock:
 		 *

@@ -1576,7 +1576,7 @@ static int validate_chain(struct task_st
 #else
 static inline int validate_chain(struct task_struct *curr,
 	       	struct lockdep_map *lock, struct held_lock *hlock,
-		int chain_head)
+		int chain_head, u64 chain_key)
 {
 	return 1;
 }

@@ -2450,11 +2450,11 @@ static int __lock_acquire(struct lockdep
 		chain_head = 1;
 	}
 	chain_key = iterate_chain_key(chain_key, id);
-	curr->curr_chain_key = chain_key;
 
-	if (!validate_chain(curr, lock, hlock, chain_head))
+	if (!validate_chain(curr, lock, hlock, chain_head, chain_key))
 		return 0;
 
+	curr->curr_chain_key = chain_key;
 	curr->lockdep_depth++;
 	check_chain_key(curr);
 #ifdef CONFIG_DEBUG_LOCKDEP