linux-kernel - [PATCH 1/2] perf daemon: Force waipid for all session on SIGCHLD delivery

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Message-Id: <20210320221013.1619613-1-jolsa@kernel.org>
Date:   Sat, 20 Mar 2021 23:10:12 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ian Rogers <irogers@...gle.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>
Subject: [PATCH 1/2] perf daemon: Force waipid for all session on SIGCHLD delivery

If we don't process SIGCHLD before another comes, we will
see just one SIGCHLD as a result. In this case current code
will miss exit notification for a session and wait forever.

Adding extra waitpid check for all sessions when SIGCHLD
is received, to make sure we don't miss any session exit.

Also fix close condition for signal_fd.

Reported-by: Ian Rogers <irogers@...gle.com>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/perf/builtin-daemon.c | 50 +++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/tools/perf/builtin-daemon.c b/tools/perf/builtin-daemon.c
index ace8772a4f03..4697493842f5 100644
--- a/tools/perf/builtin-daemon.c
+++ b/tools/perf/builtin-daemon.c
@@ -402,35 +402,42 @@ static pid_t handle_signalfd(struct daemon *daemon)
 	int status;
 	pid_t pid;
 
+	/*
+	 * Take signal fd data as pure signal notification and check all
+	 * the sessions state. The reason is that multiple signals can get
+	 * coalesced in kernel and we can receive only single signal even
+	 * if multiple SIGCHLD were generated.
+	 */
 	err = read(daemon->signal_fd, &si, sizeof(struct signalfd_siginfo));
-	if (err != sizeof(struct signalfd_siginfo))
+	if (err != sizeof(struct signalfd_siginfo)) {
+		pr_err("failed to read signal fd\n");
 		return -1;
+	}
 
 	list_for_each_entry(session, &daemon->sessions, list) {
+		if (session->pid == -1)
+			continue;
 
-		if (session->pid != (int) si.ssi_pid)
+		pid = waitpid(session->pid, &status, WNOHANG);
+		if (pid <= 0)
 			continue;
 
-		pid = waitpid(session->pid, &status, 0);
-		if (pid == session->pid) {
-			if (WIFEXITED(status)) {
-				pr_info("session '%s' exited, status=%d\n",
-					session->name, WEXITSTATUS(status));
-			} else if (WIFSIGNALED(status)) {
-				pr_info("session '%s' killed (signal %d)\n",
-					session->name, WTERMSIG(status));
-			} else if (WIFSTOPPED(status)) {
-				pr_info("session '%s' stopped (signal %d)\n",
-					session->name, WSTOPSIG(status));
-			} else {
-				pr_info("session '%s' Unexpected status (0x%x)\n",
-					session->name, status);
-			}
+		if (WIFEXITED(status)) {
+			pr_info("session '%s' exited, status=%d\n",
+				session->name, WEXITSTATUS(status));
+		} else if (WIFSIGNALED(status)) {
+			pr_info("session '%s' killed (signal %d)\n",
+				session->name, WTERMSIG(status));
+		} else if (WIFSTOPPED(status)) {
+			pr_info("session '%s' stopped (signal %d)\n",
+				session->name, WSTOPSIG(status));
+		} else {
+			pr_info("session '%s' Unexpected status (0x%x)\n",
+				session->name, status);
 		}
 
 		session->state = KILL;
 		session->pid = -1;
-		return pid;
 	}
 
 	return 0;
@@ -443,7 +450,6 @@ static int daemon_session__wait(struct daemon_session *session, struct daemon *d
 		.fd	= daemon->signal_fd,
 		.events	= POLLIN,
 	};
-	pid_t wpid = 0, pid = session->pid;
 	time_t start;
 
 	start = time(NULL);
@@ -452,7 +458,7 @@ static int daemon_session__wait(struct daemon_session *session, struct daemon *d
 		int err = poll(&pollfd, 1, 1000);
 
 		if (err > 0) {
-			wpid = handle_signalfd(daemon);
+			handle_signalfd(daemon);
 		} else if (err < 0) {
 			perror("failed: poll\n");
 			return -1;
@@ -460,7 +466,7 @@ static int daemon_session__wait(struct daemon_session *session, struct daemon *d
 
 		if (start + secs < time(NULL))
 			return -1;
-	} while (wpid != pid);
+	} while (session->pid != -1);
 
 	return 0;
 }
@@ -1344,7 +1350,7 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
 		close(sock_fd);
 	if (conf_fd != -1)
 		close(conf_fd);
-	if (conf_fd != -1)
+	if (signal_fd != -1)
 		close(signal_fd);
 
 	pr_info("daemon exited\n");
-- 
2.30.2