[PATCH 1/2] lockdep: Refactor save_trace()

[Byungchul Park]

Actually, this 1/2 patch will be useful only with combining crossrelease
implementation. However, you can easily guess the way to handle
stack_trace in crossrelease with these two patches.

----->8-----
>From 8093188ebba720a1a79cd73c52e992bad7d15bfd Mon Sep 17 00:00:00 2001
From: Byungchul Park <byungchul.p...@lge.com>
Date: Fri, 13 Jan 2017 13:54:51 +0900
Subject: [PATCH 1/2] lockdep: Refactor save_trace()

Currently, save_trace() allocates a buffer for saving stack_trace from
the global buffer, and then saves the trace. However, it would be more
useful if a separate buffer can be used. Actually, crossrelease needs
to use separate temporal buffers where to save stack_traces.

Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
---
 kernel/locking/lockdep.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2081c31..e63ff97 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -392,13 +392,13 @@ static void print_lockdep_off(const char *bug_msg)
 #endif
 }
 
-static int save_trace(struct stack_trace *trace)
+static unsigned int __save_trace(struct stack_trace *trace, unsigned long *buf,
+                                unsigned long max_nr, int skip)
 {
        trace->nr_entries = 0;
-       trace->max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
-       trace->entries = stack_trace + nr_stack_trace_entries;
-
-       trace->skip = 3;
+       trace->max_entries = max_nr;
+       trace->entries = buf;
+       trace->skip = skip;
 
        save_stack_trace(trace);
 
@@ -415,7 +415,15 @@ static int save_trace(struct stack_trace *trace)
 
        trace->max_entries = trace->nr_entries;
 
-       nr_stack_trace_entries += trace->nr_entries;
+       return trace->nr_entries;
+}
+
+static int save_trace(struct stack_trace *trace)
+{
+       unsigned long *buf = stack_trace + nr_stack_trace_entries;
+       unsigned long max_nr = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
+
+       nr_stack_trace_entries += __save_trace(trace, buf, max_nr, 3);
 
        if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES-1) {
                if (!debug_locks_off_graph_unlock())
-- 
1.9.1