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

tip-bot for Ingo Molnar
2009-06-15T07:25:29Z

Commit-ID: 667d13da070a444aeb4ad4cf7b793c8c8f64dc5d
Gitweb: http://git.kernel.org/tip/667d13da070a444aeb4ad4cf7b793c8c8f64dc5d
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Mon, 15 Jun 2009 08:17:12 +0200
Committer: Ingo Molnar <mingo@elte.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@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.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);