linux-kernel - [PATCH] perf sched latency: Fix removed thread issue

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Message-Id: <1446462625-15807-1-git-send-email-jolsa@kernel.org>
Date:	Mon,  2 Nov 2015 12:10:25 +0100
From:	Jiri Olsa <jolsa@...nel.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mohit Agrawal <moagrawa@...hat.com>
Subject: [PATCH] perf sched latency: Fix removed thread issue

If machine's thread gets excited (EXIT event is received),
we set thread->dead = true and it is later on removed from
machine's tree if the pid is reused on new thread.

The latency subcommand holds tree of working atoms sorted
by thread's pid/tid. If there's new thread with same pid
and tid, the old working atom is found and assert bug
condition is hit in search function:

  thread_atoms_search: Assertion `!(thread != atoms->thread)' failed

Changing the sort function to use thread object pointers
together with pid and tid check. This way new thread will
never find old one with same pid/tid.

I think we could change this to the sort based on timestamp
of thread creation, once it's added within Namhyung's thread
patchset.

Reported-by: Mohit Agrawal <moagrawa@...hat.com>
Link: http://lkml.kernel.org/n/tip-o4doazhhv0zax5zshkg8hnys@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/perf/builtin-sched.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 0ee6d900e100..e3d3e32c0a93 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -1203,12 +1203,13 @@ static void output_lat_thread(struct perf_sched *sched, struct work_atoms *work_
 
 static int pid_cmp(struct work_atoms *l, struct work_atoms *r)
 {
+	if (l->thread == r->thread)
+		return 0;
 	if (l->thread->tid < r->thread->tid)
 		return -1;
 	if (l->thread->tid > r->thread->tid)
 		return 1;
-
-	return 0;
+	return (int)(l->thread - r->thread);
 }
 
 static int avg_cmp(struct work_atoms *l, struct work_atoms *r)
-- 
2.4.3

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