[tip:perf/urgent] perf namespace: Protect reading thread's namespace

[tip-bot for Namhyung Kim]

Commit-ID:  6584140ba9e6762dd7ec73795243289b914f31f9
Gitweb:     https://git.kernel.org/tip/6584140ba9e6762dd7ec73795243289b914f31f9
Author:     Namhyung Kim <namhyung@xxxxxxxxxx>
AuthorDate: Wed, 22 May 2019 14:32:48 +0900
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Tue, 28 May 2019 09:52:23 -0300

perf namespace: Protect reading thread's namespace

It seems that the current code lacks holding the namespace lock in
thread__namespaces().  Otherwise it can see inconsistent results.

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Hari Bathini <hbathini@xxxxxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Krister Johansen <kjlx@xxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20190522053250.207156-2-namhyung@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/thread.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index 403045a2bbea..b413ba5b9835 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -133,7 +133,7 @@ void thread__put(struct thread *thread)
 	}
 }
 
-struct namespaces *thread__namespaces(const struct thread *thread)
+static struct namespaces *__thread__namespaces(const struct thread *thread)
 {
 	if (list_empty(&thread->namespaces_list))
 		return NULL;
@@ -141,10 +141,21 @@ struct namespaces *thread__namespaces(const struct thread *thread)
 	return list_first_entry(&thread->namespaces_list, struct namespaces, list);
 }
 
+struct namespaces *thread__namespaces(const struct thread *thread)
+{
+	struct namespaces *ns;
+
+	down_read((struct rw_semaphore *)&thread->namespaces_lock);
+	ns = __thread__namespaces(thread);
+	up_read((struct rw_semaphore *)&thread->namespaces_lock);
+
+	return ns;
+}
+
 static int __thread__set_namespaces(struct thread *thread, u64 timestamp,
 				    struct namespaces_event *event)
 {
-	struct namespaces *new, *curr = thread__namespaces(thread);
+	struct namespaces *new, *curr = __thread__namespaces(thread);
 
 	new = namespaces__new(event);
 	if (!new)