[PATCH 2/2] lockdep: Pass a callback arg to check_prev_add() to handle stack_trace

Byungchul Park
2017-01-13T10:18:50Z

Currently, a separate stack_trace instance cannot be used in
check_prev_add(). The simplest way to achieve it is to pass a
stack_trace instance to check_prev_add() as an argument after
saving it. However, unnecessary saving can happen if so implemented.

The proper solution is to pass a callback function additionally along
with a stack_trace so that a caller can decide the way to save, for
example, doing nothing, calling save_trace() or doing something else.

Actually, crossrelease don't need to save stack_trace of current but
only need to copy stack_traces from temporary buffers to the global
stack_trace[].

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/locking/lockdep.c | 38 ++++++++++++++++++--------------------
1 file changed, 18 insertions(+), 20 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e63ff97..75dc14a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1805,20 +1805,13 @@ static inline void inc_chains(void)
*/
static int
check_prev_add(struct task_struct *curr, struct held_lock *prev,
- struct held_lock *next, int distance, int *stack_saved)
+ struct held_lock *next, int distance, struct stack_trace *trace,
+ int (*save)(struct stack_trace *trace))
{
struct lock_list *entry;
int ret;
struct lock_list this;
struct lock_list *uninitialized_var(target_entry);
- /*
- * Static variable, serialized by the graph_lock().
- *
- * We use this static variable to save the stack trace in case
- * we call into this function multiple times due to encountering
- * trylocks in the held lock stack.
- */
- static struct stack_trace trace;

/*
* Prove that the new <prev> -> <next> dependency would not
@@ -1866,11 +1859,8 @@ static inline void inc_chains(void)
}
}

- if (!*stack_saved) {
- if (!save_trace(&trace))
- return 0;
- *stack_saved = 1;
- }
+ if (save && !save(trace))
+ return 0;

/*
* Ok, all validations passed, add the new lock
@@ -1878,14 +1868,14 @@ static inline void inc_chains(void)
*/
ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
&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(next), hlock_class(prev),
&hlock_class(next)->locks_before,
- next->acquire_ip, distance, &trace);
+ next->acquire_ip, distance, trace);
if (!ret)
return 0;

@@ -1893,8 +1883,6 @@ static inline void inc_chains(void)
* Debugging printouts:
*/
if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) {
- /* We drop graph lock, so another thread can overwrite trace. */
- *stack_saved = 0;
graph_unlock();
printk("\n new dependency: ");
print_lock_name(hlock_class(prev));
@@ -1917,8 +1905,10 @@ static inline void inc_chains(void)
check_prevs_add(struct task_struct *curr, struct held_lock *next)
{
int depth = curr->lockdep_depth;
- int stack_saved = 0;
struct held_lock *hlock;
+ struct stack_trace trace;
+ unsigned long start_nr = nr_stack_trace_entries;
+ int (*save)(struct stack_trace *trace) = save_trace;

/*
* Debugging checks.
@@ -1944,8 +1934,16 @@ static inline void inc_chains(void)
*/
if (hlock->read != 2 && hlock->check) {
if (!check_prev_add(curr, hlock, next,
- distance, &stack_saved))
+ distance, &trace, save))
return 0;
+
+ /*
+ * Stop saving stack_trace if save_trace() was
+ * called at least once:
+ */
+ if (save && start_nr != nr_stack_trace_entries)
+ save = NULL;
+
/*
* Stop after the first non-trylock entry,
* as non-trylock entries have added their
--
1.9.1