X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=src%2Flib%2Flttng-ust%2Flttng-ust-comm.c;h=10883e9675b6374f42bfa38d0b7529eb8cbc05e1;hb=a987943be74e59e0383b7a5b4b5fa2c47c3ab578;hp=25d79d9f4dce4fc7f3f4518e796e270fa8fcf78a;hpb=4d03f5699ca5129319b8ceb7baef85bbf05f3f3e;p=lttng-ust.git

diff --git a/src/lib/lttng-ust/lttng-ust-comm.c b/src/lib/lttng-ust/lttng-ust-comm.c
index 25d79d9f..10883e96 100644
--- a/src/lib/lttng-ust/lttng-ust-comm.c
+++ b/src/lib/lttng-ust/lttng-ust-comm.c
@@ -1,7 +1,7 @@
 /*
  * SPDX-License-Identifier: LGPL-2.1-only
  *
- * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
+ * Copyright (C) 2011 EfficiOS Inc.
  * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  */
 
@@ -38,6 +38,7 @@
 #include <lttng/ust-thread.h>
 #include <lttng/ust-tracer.h>
 #include <lttng/ust-common.h>
+#include <lttng/ust-cancelstate.h>
 #include <urcu/tls-compat.h>
 #include "lib/lttng-ust/futex.h"
 #include "common/ustcomm.h"
@@ -117,6 +118,28 @@ static int lttng_ust_comm_should_quit;
  */
 int lttng_ust_loaded __attribute__((weak));
 
+/*
+ * Notes on async-signal-safety of ust lock: a few libc functions are used
+ * which are not strictly async-signal-safe:
+ *
+ * - pthread_setcancelstate
+ * - pthread_mutex_lock
+ * - pthread_mutex_unlock
+ *
+ * As of glibc 2.35, the implementation of pthread_setcancelstate only
+ * touches TLS data, and it appears to be safe to use from signal
+ * handlers. If the libc implementation changes, this will need to be
+ * revisited, and we may ask glibc to provide an async-signal-safe
+ * pthread_setcancelstate.
+ *
+ * As of glibc 2.35, the implementation of pthread_mutex_lock/unlock
+ * for fast mutexes only relies on the pthread_mutex_t structure.
+ * Disabling signals around all uses of this mutex ensures
+ * signal-safety. If the libc implementation changes and eventually uses
+ * other global resources, this will need to be revisited and we may
+ * need to implement our own mutex.
+ */
+
 /*
  * Return 0 on success, -1 if should quit.
  * The lock is taken in both cases.
@@ -125,25 +148,21 @@ int lttng_ust_loaded __attribute__((weak));
 int ust_lock(void)
 {
 	sigset_t sig_all_blocked, orig_mask;
-	int ret, oldstate;
+	int ret;
 
-	ret = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
-	if (ret) {
-		ERR("pthread_setcancelstate: %s", strerror(ret));
-	}
-	if (oldstate != PTHREAD_CANCEL_ENABLE) {
-		ERR("pthread_setcancelstate: unexpected oldstate");
+	if (lttng_ust_cancelstate_disable_push()) {
+		ERR("lttng_ust_cancelstate_disable_push");
 	}
 	sigfillset(&sig_all_blocked);
 	ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
 	if (ret) {
-		ERR("pthread_sigmask: %s", strerror(ret));
+		ERR("pthread_sigmask: ret=%d", ret);
 	}
 	if (!URCU_TLS(ust_mutex_nest)++)
 		pthread_mutex_lock(&ust_mutex);
 	ret = pthread_sigmask(SIG_SETMASK, &orig_mask, NULL);
 	if (ret) {
-		ERR("pthread_sigmask: %s", strerror(ret));
+		ERR("pthread_sigmask: ret=%d", ret);
 	}
 	if (lttng_ust_comm_should_quit) {
 		return -1;
@@ -161,25 +180,21 @@ int ust_lock(void)
 void ust_lock_nocheck(void)
 {
 	sigset_t sig_all_blocked, orig_mask;
-	int ret, oldstate;
+	int ret;
 
-	ret = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
-	if (ret) {
-		ERR("pthread_setcancelstate: %s", strerror(ret));
-	}
-	if (oldstate != PTHREAD_CANCEL_ENABLE) {
-		ERR("pthread_setcancelstate: unexpected oldstate");
+	if (lttng_ust_cancelstate_disable_push()) {
+		ERR("lttng_ust_cancelstate_disable_push");
 	}
 	sigfillset(&sig_all_blocked);
 	ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
 	if (ret) {
-		ERR("pthread_sigmask: %s", strerror(ret));
+		ERR("pthread_sigmask: ret=%d", ret);
 	}
 	if (!URCU_TLS(ust_mutex_nest)++)
 		pthread_mutex_lock(&ust_mutex);
 	ret = pthread_sigmask(SIG_SETMASK, &orig_mask, NULL);
 	if (ret) {
-		ERR("pthread_sigmask: %s", strerror(ret));
+		ERR("pthread_sigmask: ret=%d", ret);
 	}
 }
 
@@ -189,25 +204,21 @@ void ust_lock_nocheck(void)
 void ust_unlock(void)
 {
 	sigset_t sig_all_blocked, orig_mask;
-	int ret, oldstate;
+	int ret;
 
 	sigfillset(&sig_all_blocked);
 	ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
 	if (ret) {
-		ERR("pthread_sigmask: %s", strerror(ret));
+		ERR("pthread_sigmask: ret=%d", ret);
 	}
 	if (!--URCU_TLS(ust_mutex_nest))
 		pthread_mutex_unlock(&ust_mutex);
 	ret = pthread_sigmask(SIG_SETMASK, &orig_mask, NULL);
 	if (ret) {
-		ERR("pthread_sigmask: %s", strerror(ret));
-	}
-	ret = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &oldstate);
-	if (ret) {
-		ERR("pthread_setcancelstate: %s", strerror(ret));
+		ERR("pthread_sigmask: ret=%d", ret);
 	}
-	if (oldstate != PTHREAD_CANCEL_DISABLE) {
-		ERR("pthread_setcancelstate: unexpected oldstate");
+	if (lttng_ust_cancelstate_disable_pop()) {
+		ERR("lttng_ust_cancelstate_disable_pop");
 	}
 }