perf tools: Avoid deadlock when map_groups are broken

Attempting to clone map groups onto themselves will deadlock.

It only happens because of other bugs, but the code should protect
itself anyway.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1439994561-27436-2-git-send-email-adrian.hunter@intel.com
[ Use pr_debug() instead of dump_fprintf() ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index 28c4b746baa1..0a9ae8014729 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -191,6 +191,12 @@ static int thread__clone_map_groups(struct thread *thread,
         if (thread->pid_ == parent->pid_)
                 return 0;
 
+        if (thread->mg == parent->mg) {
+                pr_debug("broken map groups on thread %d/%d parent %d/%d\n",
+                         thread->pid_, thread->tid, parent->pid_, parent->tid);
+                return 0;
+        }
+
         /* 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)