[PATCH 2/5] locking/lockdep: Track leaked chain_hlocks entries

[Waiman Long]

If a lock chain contains a class that is zapped, the whole lock chain is
now invalid. There is no point in keeping a partial chain behind hoping
it can be useful. So just dump the corresponding chain_hlocks entries
and account for them in a new nr_leaked_chain_hlocks stat counter which
is shown as part of /proc/lockdep_stats.

This patch also changes the type of nr_chain_hlocks to unsigned integer
to be consistent with the other counters.

A latter patch will try to reuse the freed chain_hlocks entries.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 kernel/locking/lockdep.c           | 40 ++++++------------------------
 kernel/locking/lockdep_internals.h |  5 ++--
 kernel/locking/lockdep_proc.c      |  4 ++-
 3 files changed, 14 insertions(+), 35 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c8d0374101b0..d03503b348f1 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2624,8 +2624,9 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 
 struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
 static DECLARE_BITMAP(lock_chains_in_use, MAX_LOCKDEP_CHAINS);
-int nr_chain_hlocks;
 static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
+unsigned int nr_chain_hlocks;
+unsigned int nr_leaked_chain_hlocks;
 
 struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
 {
@@ -4770,57 +4771,32 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
 					 struct lock_class *class)
 {
 #ifdef CONFIG_PROVE_LOCKING
-	struct lock_chain *new_chain;
-	u64 chain_key;
 	int i;
 
 	for (i = chain->base; i < chain->base + chain->depth; i++) {
 		if (chain_hlocks[i] != class - lock_classes)
 			continue;
-		/* The code below leaks one chain_hlock[] entry. */
-		if (--chain->depth > 0) {
-			memmove(&chain_hlocks[i], &chain_hlocks[i + 1],
-				(chain->base + chain->depth - i) *
-				sizeof(chain_hlocks[0]));
-		}
+		/* Account for leaked chain_hlock[] entries. */
+		nr_leaked_chain_hlocks += chain->depth;
+
 		/*
 		 * Each lock class occurs at most once in a lock chain so once
 		 * we found a match we can break out of this loop.
 		 */
-		goto recalc;
+		goto free_lock_chain;
 	}
 	/* Since the chain has not been modified, return. */
 	return;
 
-recalc:
-	chain_key = INITIAL_CHAIN_KEY;
-	for (i = chain->base; i < chain->base + chain->depth; i++)
-		chain_key = iterate_chain_key(chain_key, chain_hlocks[i]);
-	if (chain->depth && chain->chain_key == chain_key)
-		return;
+free_lock_chain:
 	/* Overwrite the chain key for concurrent RCU readers. */
-	WRITE_ONCE(chain->chain_key, chain_key);
+	WRITE_ONCE(chain->chain_key, INITIAL_CHAIN_KEY);
 	/*
 	 * Note: calling hlist_del_rcu() from inside a
 	 * hlist_for_each_entry_rcu() loop is safe.
 	 */
 	hlist_del_rcu(&chain->entry);
 	__set_bit(chain - lock_chains, pf->lock_chains_being_freed);
-	if (chain->depth == 0)
-		return;
-	/*
-	 * If the modified lock chain matches an existing lock chain, drop
-	 * the modified lock chain.
-	 */
-	if (lookup_chain_cache(chain_key))
-		return;
-	new_chain = alloc_lock_chain();
-	if (WARN_ON_ONCE(!new_chain)) {
-		debug_locks_off();
-		return;
-	}
-	*new_chain = *chain;
-	hlist_add_head_rcu(&new_chain->entry, chainhashentry(chain_key));
 #endif
 }
 
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index a31d16fd3c43..b6ec9595ae88 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -128,14 +128,15 @@ extern unsigned long nr_zapped_classes;
 extern unsigned long nr_list_entries;
 long lockdep_next_lockchain(long i);
 unsigned long lock_chain_count(void);
-extern int nr_chain_hlocks;
 extern unsigned long nr_stack_trace_entries;
 
 extern unsigned int nr_hardirq_chains;
 extern unsigned int nr_softirq_chains;
 extern unsigned int nr_process_chains;
-extern unsigned int max_lockdep_depth;
+extern unsigned int nr_chain_hlocks;
+extern unsigned int nr_leaked_chain_hlocks;
 
+extern unsigned int max_lockdep_depth;
 extern unsigned int max_bfs_queue_depth;
 
 #ifdef CONFIG_PROVE_LOCKING
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 82579fd7469f..aab524530115 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -271,7 +271,7 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
 #ifdef CONFIG_PROVE_LOCKING
 	seq_printf(m, " dependency chains:             %11lu [max: %lu]\n",
 			lock_chain_count(), MAX_LOCKDEP_CHAINS);
-	seq_printf(m, " dependency chain hlocks:       %11d [max: %lu]\n",
+	seq_printf(m, " dependency chain hlocks:       %11u [max: %lu]\n",
 			nr_chain_hlocks, MAX_LOCKDEP_CHAIN_HLOCKS);
 #endif
 
@@ -345,6 +345,8 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
 	seq_puts(m, "\n");
 	seq_printf(m, " zapped classes:                %11lu\n",
 			nr_zapped_classes);
+	seq_printf(m, " leaked chain hlocks:           %11u\n",
+			nr_leaked_chain_hlocks);
 	return 0;
 }
 
-- 
2.18.1