[PATCH] perf: detect loops processing events

[David Ahern <dsahern@gmail.com>]

Recovery algorithm in __perf_session__process_events attempts to remap
a perf.data file with a different file_offset and try again at a new head
position. Both of these adjustment rely on page_offset. If page_offset is
0 then file_offset and head never change which means the remap attempt is
the same and the fetch_mmaped_event is the same and the processing just
loops forever.

Detect this condition and warn the user.

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
---
 tools/perf/util/session.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index cf1fe01..1c4dc45 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1235,6 +1235,12 @@ more:
 		}
 
 		page_offset = page_size * (head / page_size);
+		/* catch looping where we never make forward progress. */
+		if (page_offset == 0) {
+			pr_err("Loop detection processing events. Is file corrupted?\n");
+			return -1;
+		}
+
 		file_offset += page_offset;
 		head -= page_offset;
 		goto remap;
-- 
1.7.10.1