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Subject[RFC patch 34/41] lockdep: Move stack trace logic into check_prev_add()
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@linutronix.de>
---
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;


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