[systemd-devel] [PATCH] gssd: Improve scalability by not waiting for child processes

[Steve Dickson]

Instead of waiting on every fork, which would
become a bottle neck during a mount storm, simply
set a SIGCHLD signal handler to do the wait on
the child process

Signed-off-by: Steve Dickson <steved at redhat.com>
---
 utils/gssd/gssd.c      | 18 ++++++++++++++++++
 utils/gssd/gssd_proc.c | 11 ++---------
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/utils/gssd/gssd.c b/utils/gssd/gssd.c
index e480349..8b778cb 100644
--- a/utils/gssd/gssd.c
+++ b/utils/gssd/gssd.c
@@ -44,11 +44,13 @@
 #define _GNU_SOURCE
 #endif
 
+#include <sys/types.h>
 #include <sys/param.h>
 #include <sys/socket.h>
 #include <sys/time.h>
 #include <sys/resource.h>
 #include <sys/inotify.h>
+#include <sys/wait.h>
 #include <rpc/rpc.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
@@ -736,6 +738,21 @@ sig_die(int signal)
 	printerr(1, "exiting on signal %d\n", signal);
 	exit(0);
 }
+static void
+sig_child(int signal)
+{
+	int err;
+	pid_t pid;
+
+	/* Parent: just wait on child to exit and return */
+	do {
+		pid = wait(&err);
+	} while(pid == -1 && errno != -ECHILD);
+
+	if (WIFSIGNALED(err))
+		printerr(0, "WARNING: forked child was killed"
+			 "with signal %d\n", WTERMSIG(err));
+}
 
 static void
 usage(char *progname)
@@ -902,6 +919,7 @@ main(int argc, char *argv[])
 
 	signal(SIGINT, sig_die);
 	signal(SIGTERM, sig_die);
+	signal(SIGCHLD, sig_child);
 	signal_set(&sighup_ev, SIGHUP, gssd_scan_cb, NULL);
 	signal_add(&sighup_ev, NULL);
 	event_set(&inotify_ev, inotify_fd, EV_READ | EV_PERSIST, gssd_inotify_cb, NULL);
diff --git a/utils/gssd/gssd_proc.c b/utils/gssd/gssd_proc.c
index 11168b2..8f5ca03 100644
--- a/utils/gssd/gssd_proc.c
+++ b/utils/gssd/gssd_proc.c
@@ -656,16 +656,9 @@ process_krb5_upcall(struct clnt_info *clp, uid_t uid, int fd, char *tgtname,
 			/* fork() failed! */
 			printerr(0, "WARNING: unable to fork() to handle"
 				"upcall: %s\n", strerror(errno));
-			return;
+			/* FALLTHROUGH */
 		default:
-			/* Parent: just wait on child to exit and return */
-			do {
-				pid = wait(&err);
-			} while(pid == -1 && errno != -ECHILD);
-
-			if (WIFSIGNALED(err))
-				printerr(0, "WARNING: forked child was killed"
-					 "with signal %d\n", WTERMSIG(err));
+			/* Parent: Return and wait for the SIGCHLD */
 			return;
 		}
 no_fork:
-- 
2.4.3