perf unwind: Call unwind__prepare_access for forked thread

Currently we call unwind__prepare_access for map event. In case we
report fork event the thread inherits its parent's maps and
unwind__prepare_access is never called for the thread.

This causes unwind__get_entries seeing uninitialized
unwind_libunwind_ops and thus returning no callchain.

Adding unwind__prepare_access calls for fork even processing.

Signed-off-by: Jiri Olsa <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: He Kuang <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/map.c

···
 #include "debug.h"
 #include "machine.h"
 #include <linux/string.h>
+#include "unwind.h"
 
 static void __maps__insert(struct maps *maps, struct map *map);
 
···
 /*
  * XXX This should not really _copy_ te maps, but refcount them.
  */
-int map_groups__clone(struct map_groups *mg,
+int map_groups__clone(struct thread *thread,
 		      struct map_groups *parent, enum map_type type)
 {
+	struct map_groups *mg = thread->mg;
 	int err = -ENOMEM;
 	struct map *map;
 	struct maps *maps = &parent->maps[type];
···
 		struct map *new = map__clone(map);
 		if (new == NULL)
 			goto out_unlock;
+
+		err = unwind__prepare_access(thread, new, NULL);
+		if (err)
+			goto out_unlock;
+
 		map_groups__insert(mg, new);
 		map__put(new);
 	}

tools/perf/util/map.h

···
                                          struct map **mapp, symbol_filter_t filter);
 void map_groups__init(struct map_groups *mg, struct machine *machine);
 void map_groups__exit(struct map_groups *mg);
-int map_groups__clone(struct map_groups *mg,
+int map_groups__clone(struct thread *thread,
 		      struct map_groups *parent, enum map_type type);
 size_t map_groups__fprintf(struct map_groups *mg, FILE *fp);
 

tools/perf/util/thread.c

···
 	return 0;
 }
 
+static int __thread__prepare_access(struct thread *thread)
+{
+	bool initialized = false;
+	int i, err = 0;
+
+	for (i = 0; i < MAP__NR_TYPES; ++i) {
+		struct maps *maps = &thread->mg->maps[i];
+		struct map *map;
+
+		pthread_rwlock_rdlock(&maps->lock);
+
+		for (map = maps__first(maps); map; map = map__next(map)) {
+			err = unwind__prepare_access(thread, map, &initialized);
+			if (err || initialized)
+				break;
+		}
+
+		pthread_rwlock_unlock(&maps->lock);
+	}
+
+	return err;
+}
+
+static int thread__prepare_access(struct thread *thread)
+{
+	int err = 0;
+
+	if (symbol_conf.use_callchain)
+		err = __thread__prepare_access(thread);
+
+	return err;
+}
+
 static int thread__clone_map_groups(struct thread *thread,
 				    struct thread *parent)
 {
···
 
 	/* This is new thread, we share map groups for process. */
 	if (thread->pid_ == parent->pid_)
-		return 0;
+		return thread__prepare_access(thread);
 
 	if (thread->mg == parent->mg) {
 		pr_debug("broken map groups on thread %d/%d parent %d/%d\n",
···
 
 	/* But this one is new process, copy maps. */
 	for (i = 0; i < MAP__NR_TYPES; ++i)
-		if (map_groups__clone(thread->mg, parent->mg, i) < 0)
+		if (map_groups__clone(thread, parent->mg, i) < 0)
 			return -ENOMEM;
 
 	return 0;