[PATCH 2/2] lockdep fixes

[Peter Zijlstra]

---
 kernel/locking/lockdep.c | 48 ++++++++++++++++++++----------------------------
 1 file changed, 20 insertions(+), 28 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 841828ba35b9..6d540bdb24b3 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1827,10 +1827,10 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	       struct held_lock *next, int distance, struct stack_trace *trace,
 	       int (*save)(struct stack_trace *trace))
 {
+	struct lock_list *uninitialized_var(target_entry);
 	struct lock_list *entry;
-	int ret;
 	struct lock_list this;
-	struct lock_list *uninitialized_var(target_entry);
+	int ret;
 
 	/*
 	 * Prove that the new <prev> -> <next> dependency would not
@@ -1844,8 +1844,17 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	this.class = hlock_class(next);
 	this.parent = NULL;
 	ret = check_noncircular(&this, hlock_class(prev), &target_entry);
-	if (unlikely(!ret))
+	if (unlikely(!ret)) {
+		if (!trace->entries) {
+			/*
+			 * If @save fails here, the printing might trigger
+			 * a WARN but because of the !nr_entries it should
+			 * not do bad things.
+			 */
+			save(trace);
+		}
 		return print_circular_bug(&this, target_entry, next, prev);
+	}
 	else if (unlikely(ret < 0))
 		return print_bfs_bug(ret);
 
@@ -1892,7 +1901,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 		return print_bfs_bug(ret);
 
 
-	if (save && !save(trace))
+	if (!trace->entries && !save(trace))
 		return 0;
 
 	/*
@@ -1912,20 +1921,6 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
 	if (!ret)
 		return 0;
 
-	/*
-	 * Debugging printouts:
-	 */
-	if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) {
-		graph_unlock();
-		printk("\n new dependency: ");
-		print_lock_name(hlock_class(prev));
-		printk(KERN_CONT " => ");
-		print_lock_name(hlock_class(next));
-		printk(KERN_CONT "\n");
-		dump_stack();
-		if (!graph_lock())
-			return 0;
-	}
 	return 2;
 }
 
@@ -1940,8 +1935,12 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 {
 	int depth = curr->lockdep_depth;
 	struct held_lock *hlock;
-	struct stack_trace trace;
-	int (*save)(struct stack_trace *trace) = save_trace;
+	struct stack_trace trace = {
+		.nr_entries = 0,
+		.max_entries = 0,
+		.entries = NULL,
+		.skip = 0,
+	};
 
 	/*
 	 * Debugging checks.
@@ -1967,18 +1966,11 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
 		 */
 		if (hlock->read != 2 && hlock->check) {
 			int ret = check_prev_add(curr, hlock, next,
-						distance, &trace, save);
+						distance, &trace, save_trace);
 			if (!ret)
 				return 0;
 
 			/*
-			 * Stop saving stack_trace if save_trace() was
-			 * called at least once:
-			 */
-			if (save && ret == 2)
-				save = NULL;
-
-			/*
 			 * Stop after the first non-trylock entry,
 			 * as non-trylock entries have added their
 			 * own direct dependencies already, so this
-- 
2.13.6


--wtgxwddho6bpjwr5--