[RFC 04/12] lockdep: Make save_trace can copy from other stack_trace

[Byungchul Park]

Currently, save_trace() can only save current context's stack trace.
However, it would be useful if it can save(copy from) another context's
stack trace. Especially, it can be used by crossrelease feature.

Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
---
 kernel/locking/lockdep.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c596bef..b03014b 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -389,7 +389,7 @@ static void print_lockdep_off(const char *bug_msg)
 #endif
 }
 
-static int save_trace(struct stack_trace *trace)
+static int save_trace(struct stack_trace *trace, struct stack_trace *copy)
 {
        trace->nr_entries = 0;
        trace->max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
@@ -397,7 +397,13 @@ static int save_trace(struct stack_trace *trace)
 
        trace->skip = 3;
 
-       save_stack_trace(trace);
+       if (copy) {
+               trace->nr_entries = min(copy->nr_entries, trace->max_entries);
+               trace->skip = copy->skip;
+               memcpy(trace->entries, copy->entries,
+                               trace->nr_entries * sizeof(unsigned long));
+       } else
+               save_stack_trace(trace);
 
        /*
         * Some daft arches put -1 at the end to indicate its a full trace.
@@ -1201,7 +1207,7 @@ static noinline int print_circular_bug(struct lock_list 
*this,
        if (!debug_locks_off_graph_unlock() || debug_locks_silent)
                return 0;
 
-       if (!save_trace(&this->trace))
+       if (!save_trace(&this->trace, NULL))
                return 0;
 
        depth = get_lock_depth(target);
@@ -1547,13 +1553,13 @@ print_bad_irq_dependency(struct task_struct *curr,
 
        printk("\nthe dependencies between %s-irq-safe lock", irqclass);
        printk(" and the holding lock:\n");
-       if (!save_trace(&prev_root->trace))
+       if (!save_trace(&prev_root->trace, NULL))
                return 0;
        print_shortest_lock_dependencies(backwards_entry, prev_root);
 
        printk("\nthe dependencies between the lock to be acquired");
        printk(" and %s-irq-unsafe lock:\n", irqclass);
-       if (!save_trace(&next_root->trace))
+       if (!save_trace(&next_root->trace, NULL))
                return 0;
        print_shortest_lock_dependencies(forwards_entry, next_root);
 
@@ -1885,7 +1891,7 @@ check_prev_add(struct task_struct *curr, struct held_lock 
*prev,
        }
 
        if (!own_trace && stack_saved && !*stack_saved) {
-               if (!save_trace(&trace))
+               if (!save_trace(&trace, NULL))
                        return 0;
                *stack_saved = 1;
        }
@@ -2436,7 +2442,7 @@ print_irq_inversion_bug(struct task_struct *curr,
        lockdep_print_held_locks(curr);
 
        printk("\nthe shortest dependencies between 2nd lock and 1st lock:\n");
-       if (!save_trace(&root->trace))
+       if (!save_trace(&root->trace, NULL))
                return 0;
        print_shortest_lock_dependencies(other, root);
 
@@ -3015,7 +3021,7 @@ static int mark_lock(struct task_struct *curr, struct 
held_lock *this,
 
        hlock_class(this)->usage_mask |= new_mask;
 
-       if (!save_trace(hlock_class(this)->usage_traces + new_bit))
+       if (!save_trace(hlock_class(this)->usage_traces + new_bit, NULL))
                return 0;
 
        switch (new_bit) {
-- 
1.9.1