linux-kernel - [PATCH] perf tools: ignore zombie process for user profile

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Date:   Wed, 14 Dec 2016 12:48:05 -0500
From:   kan.liang@...el.com
To:     acme@...nel.org, linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, jolsa@...nel.org,
        adrian.hunter@...el.com, andi@...stfloor.org,
        Kan Liang <kan.liang@...el.com>
Subject: [PATCH] perf tools: ignore zombie process for user profile

From: Kan Liang <kan.liang@...el.com>

If user has zombie process, the perf record -u will error out.
Here is an example.
 $ ./testd &
 [1] 23796
 $ sudo perf record -e cycles -u kan
 Error:
 The sys_perf_event_open() syscall returned with 3 (No such process) for
 event (cycles).
 /bin/dmesg may provide additional information.
 No CONFIG_PERF_EVENTS=y kernel support configured?

The source code of testd is as below.
 int main() {

	if (fork())
	{
		while (1);
	}
	return 0;
 }

Zombie process is dead process. It is meaningless to profile it.
It's better to ignore it for user profile.

Signed-off-by: Kan Liang <kan.liang@...el.com>
---
 tools/perf/util/thread_map.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/tools/perf/util/thread_map.c b/tools/perf/util/thread_map.c
index 40585f5..4643b69 100644
--- a/tools/perf/util/thread_map.c
+++ b/tools/perf/util/thread_map.c
@@ -89,6 +89,39 @@ struct thread_map *thread_map__new_by_tid(pid_t tid)
 	return threads;
 }
 
+static bool is_zombie_process(pid_t pid)
+{
+	char filename[PATH_MAX];
+	char comm[PATH_MAX];
+	char bf[BUFSIZ];
+	char s_state;
+	int s_pid;
+	FILE *fp;
+	ssize_t n;
+
+	snprintf(filename, sizeof(filename), "/proc/%d/stat", pid);
+	fp = fopen(filename, "r");
+	if (!fp) {
+		pr_warning("couldn't open %s\n", filename);
+		return false;
+	}
+	if (fgets(bf, sizeof(bf), fp) == NULL) {
+		pr_warning("Couldn't read stat for pid %d\n", pid);
+		fclose(fp);
+		return false;
+	}
+	fclose(fp);
+
+	n = sscanf(bf, "%d %s %c ", &s_pid, comm, &s_state);
+	if (n < 3)
+		return false;
+
+	if (s_state == 'Z')
+		return true;
+
+	return false;
+}
+
 struct thread_map *thread_map__new_by_uid(uid_t uid)
 {
 	DIR *proc;
@@ -124,6 +157,9 @@ struct thread_map *thread_map__new_by_uid(uid_t uid)
 		if (st.st_uid != uid)
 			continue;
 
+		if (is_zombie_process(pid))
+			continue;
+
 		snprintf(path, sizeof(path), "/proc/%d/task", pid);
 		items = scandir(path, &namelist, filter, NULL);
 		if (items <= 0)
-- 
2.4.3