[RFC patch 34/41] lockdep: Move stack trace logic into check_prev_add()

[Thomas Gleixner]

There is only one caller of check_prev_add() which hands in a zeroed struct
stack trace and a function pointer to save_stack(). Inside check_prev_add()
the stack_trace struct is checked for being empty, which is always
true. Based on that one code path stores a stack trace which is unused. The
comment there does not make sense either. It's all leftovers from
historical lockdep code.

Move the variable into check_prev_add() itself and cleanup the nonsensical
checks and the pointless stack trace recording.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 kernel/locking/lockdep.c |   30 ++++++++----------------------
 1 file changed, 8 insertions(+), 22 deletions(-)

--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2158,10 +2158,10 @@ check_deadlock(struct task_struct *curr,
  */
 static int
 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 held_lock *next, int distance)
 {
 	struct lock_list *uninitialized_var(target_entry);
+	struct stack_trace trace;
 	struct lock_list *entry;
 	struct lock_list this;
 	int ret;
@@ -2196,17 +2196,8 @@ check_prev_add(struct task_struct *curr,
 	this.class = hlock_class(next);
 	this.parent = NULL;
 	ret = check_noncircular(&this, hlock_class(prev), &target_entry);
-	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);
-		}
+	if (unlikely(!ret))
 		return print_circular_bug(&this, target_entry, next, prev);
-	}
 	else if (unlikely(ret < 0))
 		return print_bfs_bug(ret);
 
@@ -2253,7 +2244,7 @@ check_prev_add(struct task_struct *curr,
 		return print_bfs_bug(ret);
 
 
-	if (!trace->entries && !save(trace))
+	if (!save_trace(&trace))
 		return 0;
 
 	/*
@@ -2262,14 +2253,14 @@ check_prev_add(struct task_struct *curr,
 	 */
 	ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
 			       &hlock_class(prev)->locks_after,
-			       next->acquire_ip, distance, trace);
+			       next->acquire_ip, distance, &trace);
 
 	if (!ret)
 		return 0;
 
 	ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
 			       &hlock_class(next)->locks_before,
-			       next->acquire_ip, distance, trace);
+			       next->acquire_ip, distance, &trace);
 	if (!ret)
 		return 0;
 
@@ -2287,12 +2278,6 @@ check_prevs_add(struct task_struct *curr
 {
 	int depth = curr->lockdep_depth;
 	struct held_lock *hlock;
-	struct stack_trace trace = {
-		.nr_entries = 0,
-		.max_entries = 0,
-		.entries = NULL,
-		.skip = 0,
-	};
 
 	/*
 	 * Debugging checks.
@@ -2318,7 +2303,8 @@ check_prevs_add(struct task_struct *curr
 		 * added:
 		 */
 		if (hlock->read != 2 && hlock->check) {
-			int ret = check_prev_add(curr, hlock, next, distance, &trace, save_trace);
+			int ret = check_prev_add(curr, hlock, next, distance);
+
 			if (!ret)
 				return 0;