[PATCH v8 04/14] lockdep: Make check_prev_add() able to handle external stack_trace

[Byungchul Park]

Currently, a space for stack_trace is pinned in check_prev_add(), that
makes us not able to use external stack_trace. The simplest way to
achieve it is to pass an external stack_trace as an argument.

A more suitable solution is to pass a callback additionally along with
a stack_trace so that callers can decide the way to save or whether to
save. Actually crossrelease needs to do other than saving a stack_trace.
So pass a stack_trace and callback to handle it, to check_prev_add().

Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
---
 kernel/locking/lockdep.c | 40 +++++++++++++++++++---------------------
 1 file changed, 19 insertions(+), 21 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index b23e930..22a13f9 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1813,20 +1813,13 @@ 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
@@ -1874,11 +1867,8 @@ 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
@@ -1886,14 +1876,14 @@ static inline void inc_chains(void)
         */
        ret = add_lock_to_list(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(prev),
                               &hlock_class(next)->locks_before,
-                              next->acquire_ip, distance, &trace);
+                              next->acquire_ip, distance, trace);
        if (!ret)
                return 0;
 
@@ -1901,8 +1891,6 @@ 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));
@@ -1926,8 +1914,9 @@ 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;
+       int (*save)(struct stack_trace *trace) = save_trace;
 
        /*
         * Debugging checks.
@@ -1952,9 +1941,18 @@ static inline void inc_chains(void)
                 * added:
                 */
                if (hlock->read != 2 && hlock->check) {
-                       if (!check_prev_add(curr, hlock, next,
-                                               distance, &stack_saved))
+                       int ret = check_prev_add(curr, hlock, next,
+                                               distance, &trace, save);
+                       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
-- 
1.9.1