linux-kernel - [tip:perfcounters/core] perf record: Fix fast task-exit race

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Message-ID: <tip-667d13da070a444aeb4ad4cf7b793c8c8f64dc5d@git.kernel.org>
Date:	Mon, 15 Jun 2009 07:24:47 GMT
From:	tip-bot for Ingo Molnar <mingo@...e.hu>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com, paulus@...ba.org,
	hpa@...or.com, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	efault@....de, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:perfcounters/core] perf record: Fix fast task-exit race

Commit-ID:  667d13da070a444aeb4ad4cf7b793c8c8f64dc5d
Gitweb:     http://git.kernel.org/tip/667d13da070a444aeb4ad4cf7b793c8c8f64dc5d
Author:     Ingo Molnar <mingo@...e.hu>
AuthorDate: Mon, 15 Jun 2009 08:17:12 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Mon, 15 Jun 2009 08:17:12 +0200

perf record: Fix fast task-exit race

Recording with -a (or with -p) can race with tasks going away:

   couldn't open /proc/8440/maps

Causing an early exit() and no recording done.

Do not abort the recording session - instead just skip that task.

Also, only print the warnings under -v.

Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Mike Galbraith <efault@....de>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 tools/perf/builtin-record.c |   16 ++++++++++++----
 tools/perf/builtin-report.c |    2 ++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index a177a59..e1dfef2 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -202,8 +202,12 @@ static void pid_synthesize_comm_event(pid_t pid, int full)
 
 	fd = open(filename, O_RDONLY);
 	if (fd < 0) {
-		fprintf(stderr, "couldn't open %s\n", filename);
-		exit(EXIT_FAILURE);
+		/*
+		 * We raced with a task exiting - just return:
+		 */
+		if (verbose)
+			fprintf(stderr, "couldn't open %s\n", filename);
+		return;
 	}
 	if (read(fd, bf, sizeof(bf)) < 0) {
 		fprintf(stderr, "couldn't read %s\n", filename);
@@ -273,8 +277,12 @@ static void pid_synthesize_mmap_samples(pid_t pid)
 
 	fp = fopen(filename, "r");
 	if (fp == NULL) {
-		fprintf(stderr, "couldn't open %s\n", filename);
-		exit(EXIT_FAILURE);
+		/*
+		 * We raced with a task exiting - just return:
+		 */
+		if (verbose)
+			fprintf(stderr, "couldn't open %s\n", filename);
+		return;
 	}
 	while (1) {
 		char bf[BUFSIZ], *pbf = bf;
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index aebba56..51f38b2 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -983,6 +983,8 @@ process_overflow_event(event_t *event, unsigned long offset, unsigned long head)
 			for (i = 0; i < chain->nr; i++)
 				dprintf("..... %2d: %p\n", i, (void *)chain->ips[i]);
 		}
+		if (chain->kernel)
+			ip = chain->ips[chain->kernel-1];
 	}
 
 	dprintf(" ... thread: %s:%d\n", thread->comm, thread->pid);
--
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