X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=liblttng-ust%2Flttng-ust-comm.c;h=c6640954c6aa77d34203cbc6cda8c32eae34d7c6;hb=3327ac33b865cf2ee76934ded1c4b3b177edc3b9;hp=2d3766f1326ff407351e3d41088d2d5c0aacf094;hpb=13436238c6418c33e4eb3c3ab8e2a466f1597fd2;p=lttng-ust.git

diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index 2d3766f1..c6640954 100644
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -52,7 +52,7 @@
 #include "lttng-tracer-core.h"
 #include "compat.h"
 #include "../libringbuffer/tlsfixup.h"
-#include "../liblttng-ust-baddr/lttng-ust-baddr.h"
+#include "lttng-ust-baddr.h"
 
 /*
  * Has lttng ust comm constructor been called ?
@@ -63,11 +63,55 @@ static int initialized;
  * The ust_lock/ust_unlock lock is used as a communication thread mutex.
  * Held when handling a command, also held by fork() to deal with
  * removal of threads, and by exit path.
+ *
+ * The UST lock is the centralized mutex across UST tracing control and
+ * probe registration.
+ *
+ * ust_exit_mutex must never nest in ust_mutex.
  */
+static pthread_mutex_t ust_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+/*
+ * ust_exit_mutex protects thread_active variable wrt thread exit. It
+ * cannot be done by ust_mutex because pthread_cancel(), which takes an
+ * internal libc lock, cannot nest within ust_mutex.
+ *
+ * It never nests within a ust_mutex.
+ */
+static pthread_mutex_t ust_exit_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 /* Should the ust comm thread quit ? */
 static int lttng_ust_comm_should_quit;
 
+/*
+ * Return 0 on success, -1 if should quilt.
+ * The lock is taken in both cases.
+ */
+int ust_lock(void)
+{
+	pthread_mutex_lock(&ust_mutex);
+	if (lttng_ust_comm_should_quit) {
+		return -1;
+	} else {
+		return 0;
+	}
+}
+
+/*
+ * ust_lock_nocheck() can be used in constructors/destructors, because
+ * they are already nested within the dynamic loader lock, and therefore
+ * have exclusive access against execution of liblttng-ust destructor.
+ */
+void ust_lock_nocheck(void)
+{
+	pthread_mutex_lock(&ust_mutex);
+}
+
+void ust_unlock(void)
+{
+	pthread_mutex_unlock(&ust_mutex);
+}
+
 /*
  * Wait for either of these before continuing to the main
  * program:
@@ -108,7 +152,8 @@ struct sock_info {
 
 	char wait_shm_path[PATH_MAX];
 	char *wait_shm_mmap;
-	struct lttng_session *session_enabled;
+	/* Keep track of lazy state dump not performed yet. */
+	int statedump_pending;
 };
 
 /* Socket from app (connect) to session daemon (listen) for communication */
@@ -126,7 +171,7 @@ struct sock_info global_apps = {
 
 	.wait_shm_path = "/" LTTNG_UST_WAIT_FILENAME,
 
-	.session_enabled = NULL,
+	.statedump_pending = 0,
 };
 
 /* TODO: allow global_apps_sock_path override */
@@ -141,7 +186,7 @@ struct sock_info local_apps = {
 	.socket = -1,
 	.notify_socket = -1,
 
-	.session_enabled = NULL,
+	.statedump_pending = 0,
 };
 
 static int wait_poll_fallback;
@@ -387,6 +432,28 @@ int handle_register_done(struct sock_info *sock_info)
 	return 0;
 }
 
+/*
+ * Only execute pending statedump after the constructor semaphore has
+ * been posted by each listener thread. This means statedump will only
+ * be performed after the "registration done" command is received from
+ * each session daemon the application is connected to.
+ *
+ * This ensures we don't run into deadlock issues with the dynamic
+ * loader mutex, which is held while the constructor is called and
+ * waiting on the constructor semaphore. All operations requiring this
+ * dynamic loader lock need to be postponed using this mechanism.
+ */
+static
+void handle_pending_statedump(struct sock_info *sock_info)
+{
+	int ctor_passed = sock_info->constructor_sem_posted;
+
+	if (ctor_passed && sock_info->statedump_pending) {
+		sock_info->statedump_pending = 0;
+		lttng_handle_pending_statedump(sock_info);
+	}
+}
+
 static
 int handle_message(struct sock_info *sock_info,
 		int sock, struct ustcomm_ust_msg *lum)
@@ -397,11 +464,9 @@ int handle_message(struct sock_info *sock_info,
 	union ust_args args;
 	ssize_t len;
 
-	ust_lock();
-
 	memset(&lur, 0, sizeof(lur));
 
-	if (lttng_ust_comm_should_quit) {
+	if (ust_lock()) {
 		ret = -LTTNG_UST_ERR_EXITING;
 		goto end;
 	}
@@ -705,6 +770,14 @@ end:
 
 error:
 	ust_unlock();
+
+	/*
+	 * Performed delayed statedump operations outside of the UST
+	 * lock. We need to take the dynamic loader lock before we take
+	 * the UST lock internally within handle_pending_statedump().
+	  */
+	handle_pending_statedump(sock_info);
+
 	return ret;
 }
 
@@ -952,8 +1025,7 @@ void wait_for_sessiond(struct sock_info *sock_info)
 {
 	int ret;
 
-	ust_lock();
-	if (lttng_ust_comm_should_quit) {
+	if (ust_lock()) {
 		goto quit;
 	}
 	if (wait_poll_fallback) {
@@ -1058,9 +1130,7 @@ restart:
 		DBG("Info: sessiond not accepting connections to %s apps socket", sock_info->name);
 		prev_connect_failed = 1;
 
-		ust_lock();
-
-		if (lttng_ust_comm_should_quit) {
+		if (ust_lock()) {
 			goto quit;
 		}
 
@@ -1075,9 +1145,7 @@ restart:
 	}
 	sock_info->socket = ret;
 
-	ust_lock();
-
-	if (lttng_ust_comm_should_quit) {
+	if (ust_lock()) {
 		goto quit;
 	}
 
@@ -1118,9 +1186,7 @@ restart:
 		DBG("Info: sessiond not accepting connections to %s apps socket", sock_info->name);
 		prev_connect_failed = 1;
 
-		ust_lock();
-
-		if (lttng_ust_comm_should_quit) {
+		if (ust_lock()) {
 			goto quit;
 		}
 
@@ -1157,9 +1223,7 @@ restart:
 		WARN("Unsupported timeout value %ld", timeout);
 	}
 
-	ust_lock();
-
-	if (lttng_ust_comm_should_quit) {
+	if (ust_lock()) {
 		goto quit;
 	}
 
@@ -1190,8 +1254,7 @@ restart:
 		switch (len) {
 		case 0:	/* orderly shutdown */
 			DBG("%s lttng-sessiond has performed an orderly shutdown", sock_info->name);
-			ust_lock();
-			if (lttng_ust_comm_should_quit) {
+			if (ust_lock()) {
 				goto quit;
 			}
 			/*
@@ -1213,14 +1276,6 @@ restart:
 			ret = handle_message(sock_info, sock, &lum);
 			if (ret) {
 				ERR("Error handling message for %s socket", sock_info->name);
-			} else {
-				struct lttng_session *session;
-
-				session = sock_info->session_enabled;
-				if (session) {
-					sock_info->session_enabled = NULL;
-					lttng_ust_baddr_statedump(session);
-				}
 			}
 			continue;
 		default:
@@ -1238,8 +1293,7 @@ restart:
 
 	}
 end:
-	ust_lock();
-	if (lttng_ust_comm_should_quit) {
+	if (ust_lock()) {
 		goto quit;
 	}
 	/* Cleanup socket handles before trying to reconnect */
@@ -1248,8 +1302,11 @@ end:
 	goto restart;	/* try to reconnect */
 
 quit:
-	sock_info->thread_active = 0;
 	ust_unlock();
+
+	pthread_mutex_lock(&ust_exit_mutex);
+	sock_info->thread_active = 0;
+	pthread_mutex_unlock(&ust_exit_mutex);
 	return NULL;
 }
 
@@ -1323,7 +1380,7 @@ void __attribute__((constructor)) lttng_ust_init(void)
 		ERR("pthread_attr_setdetachstate: %s", strerror(ret));
 	}
 
-	ust_lock();
+	ust_lock_nocheck();
 	ret = pthread_create(&global_apps.ust_listener, &thread_attr,
 			ust_listener_thread, &global_apps);
 	if (ret) {
@@ -1333,7 +1390,7 @@ void __attribute__((constructor)) lttng_ust_init(void)
 	ust_unlock();
 
 	if (local_apps.allowed) {
-		ust_lock();
+		ust_lock_nocheck();
 		ret = pthread_create(&local_apps.ust_listener, &thread_attr,
 				ust_listener_thread, &local_apps);
 		if (ret) {
@@ -1424,9 +1481,11 @@ void __attribute__((destructor)) lttng_ust_exit(void)
 	 * mutexes to ensure it is not in a mutex critical section when
 	 * pthread_cancel is later called.
 	 */
-	ust_lock();
+	ust_lock_nocheck();
 	lttng_ust_comm_should_quit = 1;
+	ust_unlock();
 
+	pthread_mutex_lock(&ust_exit_mutex);
 	/* cancel threads */
 	if (global_apps.thread_active) {
 		ret = pthread_cancel(global_apps.ust_listener);
@@ -1446,7 +1505,7 @@ void __attribute__((destructor)) lttng_ust_exit(void)
 			local_apps.thread_active = 0;
 		}
 	}
-	ust_unlock();
+	pthread_mutex_unlock(&ust_exit_mutex);
 
 	/*
 	 * Do NOT join threads: use of sys_futex makes it impossible to
@@ -1485,7 +1544,7 @@ void ust_before_fork(sigset_t *save_sigset)
 	if (ret == -1) {
 		PERROR("sigprocmask");
 	}
-	ust_lock();
+	ust_lock_nocheck();
 	rcu_bp_before_fork();
 }
 
@@ -1535,9 +1594,8 @@ void ust_after_fork_child(sigset_t *restore_sigset)
 	lttng_ust_init();
 }
 
-void lttng_ust_sockinfo_session_enabled(void *owner,
-		struct lttng_session *session_enabled)
+void lttng_ust_sockinfo_session_enabled(void *owner)
 {
 	struct sock_info *sock_info = owner;
-	sock_info->session_enabled = session_enabled;
+	sock_info->statedump_pending = 1;
 }