linux-kernel - [PATCH] perf: detect loops processing events

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Date:	Wed,  8 May 2013 09:18:47 -0600
From:	David Ahern <dsahern@...il.com>
To:	acme@...stprotocols.net, linux-kernel@...r.kernel.org
Cc:	David Ahern <dsahern@...il.com>, Ingo Molnar <mingo@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: [PATCH] perf: detect loops processing events

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@...il.com>
Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Stephane Eranian <eranian@...gle.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

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