[dpdk-dev] [PATCH 3/3] eal: use locks to determine if secondary process is active

[Anatoly Burakov <anatoly.burakov@intel.com>]

Previously, IPC would remove sockets it considers to be "inactive"
based on whether they have responded. Change this to create lock
files in addition to socket files, so that we can determine if
secondary process is active before attempting to communicate with
it. That way, we can distinguish secondaries that are alive but
are not responding, from those that have already died.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
---
 lib/librte_eal/common/eal_common_proc.c | 204 +++++++++++++++++++++++++++-----
 1 file changed, 175 insertions(+), 29 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_proc.c b/lib/librte_eal/common/eal_common_proc.c
index b4d00c3..17fded7 100644
--- a/lib/librte_eal/common/eal_common_proc.c
+++ b/lib/librte_eal/common/eal_common_proc.c
@@ -13,6 +13,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/file.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -32,6 +33,7 @@
 #include "eal_internal_cfg.h"
 
 static int mp_fd = -1;
+static int lock_fd = -1;
 static char mp_filter[PATH_MAX];   /* Filter for secondary process sockets */
 static char mp_dir_path[PATH_MAX]; /* The directory path for all mp sockets */
 static pthread_mutex_t mp_mutex_action = PTHREAD_MUTEX_INITIALIZER;
@@ -104,6 +106,46 @@ find_sync_request(const char *dst, const char *act_name)
 	return r;
 }
 
+static void
+create_socket_path(const char *name, char *buf, int len)
+{
+	const char *prefix = eal_mp_socket_path();
+	if (strlen(name) > 0)
+		snprintf(buf, len, "%s_%s", prefix, name);
+	else
+		snprintf(buf, len, "%s", prefix);
+}
+
+static void
+create_lockfile_path(const char *name, char *buf, int len)
+{
+	const char *prefix = eal_mp_socket_path();
+	if (strlen(name) > 1)
+		snprintf(buf, len, "%slock_%s", prefix, name);
+	else
+		snprintf(buf, len, "%slock", prefix);
+}
+
+static const char *
+get_peer_name(const char *socket_full_path)
+{
+	char buf[PATH_MAX] = {0};
+	int len;
+
+	/* primary process has no peer name */
+	if (strcmp(socket_full_path, eal_mp_socket_path()) == 0)
+		return NULL;
+
+	/* construct dummy socket file name - make it one character long so that
+	 * we hit the code path where underscores are added
+	 */
+	create_socket_path("a", buf, sizeof(buf));
+
+	/* we want to get everything after /path/.rte_unix_, so discard 'a' */
+	len = strlen(buf) - 1;
+	return &socket_full_path[len];
+}
+
 int
 rte_eal_primary_proc_alive(const char *config_file_path)
 {
@@ -330,8 +372,29 @@ mp_handle(void *arg __rte_unused)
 static int
 open_socket_fd(void)
 {
+	char peer_name[PATH_MAX] = {0};
+	char lockfile[PATH_MAX] = {0};
 	struct sockaddr_un un;
-	const char *prefix = eal_mp_socket_path();
+
+	if (rte_eal_process_type() == RTE_PROC_SECONDARY)
+		snprintf(peer_name, sizeof(peer_name), "%d_%"PRIx64,
+			 getpid(), rte_rdtsc());
+
+	/* try to create lockfile */
+	create_lockfile_path(peer_name, lockfile, sizeof(lockfile));
+
+	lock_fd = open(lockfile, O_CREAT | O_RDWR);
+	if (lock_fd < 0) {
+		RTE_LOG(ERR, EAL, "failed to open '%s': %s\n", lockfile,
+			strerror(errno));
+		return -1;
+	}
+	if (flock(lock_fd, LOCK_EX | LOCK_NB)) {
+		RTE_LOG(ERR, EAL, "failed to lock '%s': %s\n", lockfile,
+			strerror(errno));
+		return -1;
+	}
+	/* no need to downgrade to shared lock */
 
 	mp_fd = socket(AF_UNIX, SOCK_DGRAM, 0);
 	if (mp_fd < 0) {
@@ -341,13 +404,11 @@ open_socket_fd(void)
 
 	memset(&un, 0, sizeof(un));
 	un.sun_family = AF_UNIX;
-	if (rte_eal_process_type() == RTE_PROC_PRIMARY)
-		snprintf(un.sun_path, sizeof(un.sun_path), "%s", prefix);
-	else {
-		snprintf(un.sun_path, sizeof(un.sun_path), "%s_%d_%"PRIx64,
-			 prefix, getpid(), rte_rdtsc());
-	}
+
+	create_socket_path(peer_name, un.sun_path, sizeof(un.sun_path));
+
 	unlink(un.sun_path); /* May still exist since last run */
+
 	if (bind(mp_fd, (struct sockaddr *)&un, sizeof(un)) < 0) {
 		RTE_LOG(ERR, EAL, "failed to bind %s: %s\n",
 			un.sun_path, strerror(errno));
@@ -359,6 +420,44 @@ open_socket_fd(void)
 	return mp_fd;
 }
 
+/* find corresponding lock file and try to lock it */
+static int
+socket_is_active(const char *peer_name)
+{
+	char lockfile[PATH_MAX] = {0};
+	int fd, ret = -1;
+
+	/* construct lockfile filename */
+	create_lockfile_path(peer_name, lockfile, sizeof(lockfile));
+
+	/* try to lock it */
+	fd = open(lockfile, O_CREAT | O_RDWR);
+	if (fd < 0) {
+		RTE_LOG(ERR, EAL, "Cannot open '%s': %s\n", lockfile,
+			strerror(errno));
+		return -1;
+	}
+	ret = flock(fd, LOCK_EX | LOCK_NB);
+	if (ret < 0) {
+		if (errno == EWOULDBLOCK) {
+			/* file is locked */
+			ret = 1;
+		} else {
+			RTE_LOG(ERR, EAL, "Cannot lock '%s': %s\n", lockfile,
+				strerror(errno));
+			ret = -1;
+		}
+	} else {
+		ret = 0;
+		/* unlink lockfile automatically */
+		unlink(lockfile);
+		flock(fd, LOCK_UN);
+	}
+	close(fd);
+
+	return ret;
+}
+
 static int
 unlink_sockets(const char *filter)
 {
@@ -374,28 +473,33 @@ unlink_sockets(const char *filter)
 	dir_fd = dirfd(mp_dir);
 
 	while ((ent = readdir(mp_dir))) {
-		if (fnmatch(filter, ent->d_name, 0) == 0)
+		if (fnmatch(filter, ent->d_name, 0) == 0) {
+			const char *peer_name;
+			char path[PATH_MAX];
+			int ret;
+
+			snprintf(path, sizeof(path), "%s/%s", mp_dir_path,
+				 ent->d_name);
+			peer_name = get_peer_name(path);
+
+			ret = socket_is_active(peer_name);
+			if (ret < 0) {
+				RTE_LOG(ERR, EAL, "Error getting socket active status\n");
+				return -1;
+			} else if (ret == 1) {
+				RTE_LOG(ERR, EAL, "Socket is active (old secondary process still running?)\n");
+				return -1;
+			}
+			RTE_LOG(DEBUG, EAL, "Removing stale socket file '%s'\n",
+					ent->d_name);
 			unlinkat(dir_fd, ent->d_name, 0);
+		}
 	}
 
 	closedir(mp_dir);
 	return 0;
 }
 
-static void
-unlink_socket_by_path(const char *path)
-{
-	char *filename;
-	char *fullpath = strdup(path);
-
-	if (!fullpath)
-		return;
-	filename = basename(fullpath);
-	unlink_sockets(filename);
-	free(fullpath);
-	RTE_LOG(INFO, EAL, "Remove socket %s\n", path);
-}
-
 int
 rte_mp_channel_init(void)
 {
@@ -485,10 +589,25 @@ send_msg(const char *dst_path, struct rte_mp_msg *msg, int type)
 		rte_errno = errno;
 		/* Check if it caused by peer process exits */
 		if (errno == ECONNREFUSED) {
-			/* We don't unlink the primary's socket here */
-			if (rte_eal_process_type() == RTE_PROC_PRIMARY)
-				unlink_socket_by_path(dst_path);
-			return 0;
+			const char *peer_name = get_peer_name(dst_path);
+			int active, ret = 0;
+
+			active = rte_eal_process_type() == RTE_PROC_PRIMARY ?
+					socket_is_active(peer_name) :
+					rte_eal_primary_proc_alive(NULL);
+
+			if (active > 0) {
+				RTE_LOG(ERR, EAL, "Couldn't communicate with active peer\n");
+			} else if (active < 0) {
+				RTE_LOG(ERR, EAL, "Couldn't get peer status\n");
+				ret = -1;
+			} else if (rte_eal_process_type() == RTE_PROC_PRIMARY) {
+				/* peer isn't active anymore, so unlink its
+				 * socket.
+				 */
+				unlink(dst_path);
+			}
+			return ret;
 		}
 		if (errno == ENOBUFS) {
 			RTE_LOG(ERR, EAL, "Peer cannot receive message %s\n",
@@ -506,7 +625,7 @@ send_msg(const char *dst_path, struct rte_mp_msg *msg, int type)
 static int
 mp_send(struct rte_mp_msg *msg, const char *peer, int type)
 {
-	int ret = 0;
+	int dir_fd, ret = 0;
 	DIR *mp_dir;
 	struct dirent *ent;
 
@@ -528,15 +647,28 @@ mp_send(struct rte_mp_msg *msg, const char *peer, int type)
 		rte_errno = errno;
 		return -1;
 	}
+	dir_fd = dirfd(mp_dir);
 	while ((ent = readdir(mp_dir))) {
 		char path[PATH_MAX];
+		const char *peer_name;
+		int active;
 
 		if (fnmatch(mp_filter, ent->d_name, 0) != 0)
 			continue;
 
 		snprintf(path, sizeof(path), "%s/%s", mp_dir_path,
 			 ent->d_name);
-		if (send_msg(path, msg, type) < 0)
+		peer_name = get_peer_name(path);
+
+		/* only send if we can expect to receive a reply, otherwise
+		 * remove the socket.
+		 */
+		active = socket_is_active(peer_name);
+		if (active < 0)
+			ret = -1;
+		else if (active == 0)
+			unlinkat(dir_fd, ent->d_name, 0);
+		else if (active > 0 && send_msg(path, msg, type) < 0)
 			ret = -1;
 	}
 
@@ -661,7 +793,7 @@ int __rte_experimental
 rte_mp_request(struct rte_mp_msg *req, struct rte_mp_reply *reply,
 		const struct timespec *ts)
 {
-	int ret = 0;
+	int dir_fd, ret = 0;
 	DIR *mp_dir;
 	struct dirent *ent;
 	struct timeval now;
@@ -696,15 +828,29 @@ rte_mp_request(struct rte_mp_msg *req, struct rte_mp_reply *reply,
 		rte_errno = errno;
 		return -1;
 	}
+	dir_fd = dirfd(mp_dir);
 
 	while ((ent = readdir(mp_dir))) {
+		const char *peer_name;
 		char path[PATH_MAX];
+		int active;
 
 		if (fnmatch(mp_filter, ent->d_name, 0) != 0)
 			continue;
 
 		snprintf(path, sizeof(path), "%s/%s", mp_dir_path,
 			 ent->d_name);
+		peer_name = get_peer_name(path);
+
+		active = socket_is_active(peer_name);
+
+		if (active < 0) {
+			ret = -1;
+			break;
+		} else if (active == 0) {
+			unlinkat(dir_fd, ent->d_name, 0);
+			continue;
+		}
 
 		if (mp_request_one(path, req, reply, &end))
 			ret = -1;
-- 
2.7.4