[PATCH 20/28] locking/lockdep: Refactorize check_noncircular and check_redundant

[Yuyang Du]

These two functions now handle different check results themselves. A new
check_path function is added to check whether there is a path in the
dependency graph. No functional change.

Signed-off-by: Yuyang Du <duyuyang@xxxxxxxxx>
---
 kernel/locking/lockdep.c | 98 +++++++++++++++++++++++++++++++-----------------
 1 file changed, 63 insertions(+), 35 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index a3138c9..4d42124 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1681,33 +1681,79 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
 }
 
 /*
- * Prove that the dependency graph starting at <entry> can not
- * lead to <target>. Print an error and return 0 if it does.
+ * Check that the dependency graph starting at <src> can lead to
+ * <target> or not. Print an error and return 0 if it does.
  */
 static noinline int
-check_noncircular(struct lock_list *root, struct lock_class *target,
-		struct lock_list **target_entry)
+check_path(struct lock_class *target, struct lock_list *src_entry,
+	   struct lock_list **target_entry)
 {
-	int result;
+	int ret;
+
+	ret = __bfs_forwards(src_entry, (void *)target, class_equal,
+			     target_entry);
+
+	if (unlikely(ret < 0))
+		print_bfs_bug(ret);
+
+	return ret;
+}
+
+/*
+ * Prove that the dependency graph starting at <src> can not
+ * lead to <target>. If it can, there is a circle when adding
+ * <target> -> <src> dependency.
+ *
+ * Print an error and return 0 if it does.
+ */
+static noinline int
+check_noncircular(struct held_lock *src, struct held_lock *target)
+{
+	int ret;
+	struct lock_list *uninitialized_var(target_entry);
+	struct lock_list src_entry = {
+		.class = hlock_class(src),
+		.parent = NULL,
+	};
 
 	debug_atomic_inc(nr_cyclic_checks);
 
-	result = __bfs_forwards(root, target, class_equal, target_entry);
+	ret = check_path(hlock_class(target), &src_entry, &target_entry);
 
-	return result;
+	if (unlikely(!ret))
+		print_circular_bug(&src_entry, target_entry, src, target);
+
+	return ret;
 }
 
+/*
+ * Check that the dependency graph starting at <src> can lead to
+ * <target> or not. If it can, <src> -> <target> dependency is already
+ * in the graph.
+ *
+ * Print an error and return 2 if it does or 1 if it does not.
+ */
 static noinline int
-check_redundant(struct lock_list *root, struct lock_class *target,
-		struct lock_list **target_entry)
+check_redundant(struct held_lock *src, struct held_lock *target)
 {
-	int result;
+	int ret;
+	struct lock_list *uninitialized_var(target_entry);
+	struct lock_list src_entry = {
+		.class = hlock_class(src),
+		.parent = NULL,
+	};
 
 	debug_atomic_inc(nr_redundant_checks);
 
-	result = __bfs_forwards(root, target, class_equal, target_entry);
+	ret = check_path(hlock_class(target), &src_entry, &target_entry);
 
-	return result;
+	if (!ret) {
+		debug_atomic_inc(nr_redundant);
+		ret = 2;
+	} else if (ret < 0)
+		ret = 0;
+
+	return ret;
 }
 
 #if defined(CONFIG_TRACE_IRQFLAGS)
@@ -2208,9 +2254,7 @@ static inline void inc_chains(void)
 check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	       struct held_lock *next, int distance)
 {
-	struct lock_list *uninitialized_var(target_entry);
 	struct lock_list *entry;
-	struct lock_list this;
 	struct lock_trace trace;
 	int ret;
 
@@ -2242,17 +2286,9 @@ static inline void inc_chains(void)
 	 * MAX_CIRCULAR_QUEUE_SIZE) which keeps track of a breadth of nodes
 	 * in the graph whose neighbours are to be checked.
 	 */
-	this.class = hlock_class(next);
-	this.parent = NULL;
-	ret = check_noncircular(&this, hlock_class(prev), &target_entry);
-	if (unlikely(!ret)) {
-		print_circular_bug(&this, target_entry, next, prev);
-		return 0;
-	}
-	else if (unlikely(ret < 0)) {
-		print_bfs_bug(ret);
+	ret = check_noncircular(next, prev);
+	if (unlikely(ret <= 0))
 		return 0;
-	}
 
 	if (!check_prev_add_irq(curr, prev, next))
 		return 0;
@@ -2286,17 +2322,9 @@ static inline void inc_chains(void)
 	/*
 	 * Is the <prev> -> <next> link redundant?
 	 */
-	this.class = hlock_class(prev);
-	this.parent = NULL;
-	ret = check_redundant(&this, hlock_class(next), &target_entry);
-	if (!ret) {
-		debug_atomic_inc(nr_redundant);
-		return 2;
-	}
-	if (ret < 0) {
-		print_bfs_bug(ret);
-		return 0;
-	}
+	ret = check_redundant(prev, next);
+	if (ret != 1)
+		return ret;
 
 	if (!save_trace(&trace))
 		return 0;
-- 
1.8.3.1