[PATCH v6 10/16] locking/lockdep: Introduce lockdep_next_lockchain() and lock_chain_count()

[Bart Van Assche <bvanassche@acm.org>]

This patch does not change any functionality but makes the next patch in
this series easier to read.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 kernel/locking/lockdep.c           | 16 +++++++++++++++-
 kernel/locking/lockdep_internals.h |  3 ++-
 kernel/locking/lockdep_proc.c      | 12 ++++++------
 3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 5e8a3a17bb94..ef3809e21fa9 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2110,7 +2110,7 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 	return 0;
 }
 
-unsigned long nr_lock_chains;
+static unsigned long nr_lock_chains;
 struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
 int nr_chain_hlocks;
 static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
@@ -2244,6 +2244,20 @@ static int check_no_collision(struct task_struct *curr,
 	return 1;
 }
 
+/*
+ * Given an index that is >= -1, return the index of the next lock chain.
+ * Return -2 if there is no next lock chain.
+ */
+long lockdep_next_lockchain(long i)
+{
+	return i + 1 < nr_lock_chains ? i + 1 : -2;
+}
+
+unsigned long lock_chain_count(void)
+{
+	return nr_lock_chains;
+}
+
 /*
  * Adds a dependency chain into chain hashtable. And must be called with
  * graph_lock held.
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 88c847a41c8a..ba8a4ac7bd04 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -96,7 +96,8 @@ struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i);
 
 extern unsigned long nr_lock_classes;
 extern unsigned long nr_list_entries;
-extern unsigned long nr_lock_chains;
+long lockdep_next_lockchain(long i);
+unsigned long lock_chain_count(void);
 extern int nr_chain_hlocks;
 extern unsigned long nr_stack_trace_entries;
 
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index 3d31f9b0059e..9c49ec645d8b 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -104,18 +104,18 @@ static const struct seq_operations lockdep_ops = {
 #ifdef CONFIG_PROVE_LOCKING
 static void *lc_start(struct seq_file *m, loff_t *pos)
 {
+	if (*pos < 0)
+		return NULL;
+
 	if (*pos == 0)
 		return SEQ_START_TOKEN;
 
-	if (*pos - 1 < nr_lock_chains)
-		return lock_chains + (*pos - 1);
-
-	return NULL;
+	return lock_chains + (*pos - 1);
 }
 
 static void *lc_next(struct seq_file *m, void *v, loff_t *pos)
 {
-	(*pos)++;
+	*pos = lockdep_next_lockchain(*pos - 1) + 1;
 	return lc_start(m, pos);
 }
 
@@ -268,7 +268,7 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
 
 #ifdef CONFIG_PROVE_LOCKING
 	seq_printf(m, " dependency chains:             %11lu [max: %lu]\n",
-			nr_lock_chains, MAX_LOCKDEP_CHAINS);
+			lock_chain_count(), MAX_LOCKDEP_CHAINS);
 	seq_printf(m, " dependency chain hlocks:       %11d [max: %lu]\n",
 			nr_chain_hlocks, MAX_LOCKDEP_CHAIN_HLOCKS);
 #endif
-- 
2.20.1.97.g81188d93c3-goog