X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=src%2Furcu.c;h=c60307e15351241dbb0158b5d48d589852fcca65;hb=90f72b8c054ca4e3b4b45f630549c784e26ce79a;hp=2c9e5d1da18f531393cd603d6c6d33fa57461a2b;hpb=a0ec6d9b6b67e37fc81c98e04008907bc500cde8;p=urcu.git

diff --git a/src/urcu.c b/src/urcu.c
index 2c9e5d1..c60307e 100644
--- a/src/urcu.c
+++ b/src/urcu.c
@@ -30,7 +30,6 @@
 #include <stdio.h>
 #include <pthread.h>
 #include <signal.h>
-#include <assert.h>
 #include <stdlib.h>
 #include <stdint.h>
 #include <string.h>
@@ -39,6 +38,7 @@
 #include <poll.h>
 
 #include <urcu/config.h>
+#include <urcu/assert.h>
 #include <urcu/arch.h>
 #include <urcu/wfcqueue.h>
 #include <urcu/map/urcu.h>
@@ -109,9 +109,13 @@ void rcu_init(void)
 static int init_done;
 
 void __attribute__((constructor)) rcu_init(void);
-void __attribute__((destructor)) rcu_exit(void);
+
+static DEFINE_URCU_TLS(int, rcu_signal_was_blocked);
 #endif
 
+void __attribute__((destructor)) rcu_exit(void);
+static void urcu_call_rcu_exit(void);
+
 /*
  * rcu_gp_lock ensures mutual exclusion between threads calling
  * synchronize_rcu().
@@ -259,17 +263,25 @@ static void wait_gp(void)
 	smp_mb_master();
 	/* Temporarily unlock the registry lock. */
 	mutex_unlock(&rcu_registry_lock);
-	if (uatomic_read(&rcu_gp.futex) != -1)
-		goto end;
-	while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
-			NULL, NULL, 0)) {
+	while (uatomic_read(&rcu_gp.futex) == -1) {
+		if (!futex_async(&rcu_gp.futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
+			/*
+			 * Prior queued wakeups queued by unrelated code
+			 * using the same address can cause futex wait to
+			 * return 0 even through the futex value is still
+			 * -1 (spurious wakeups). Check the value again
+			 * in user-space to validate whether it really
+			 * differs from -1.
+			 */
+			continue;
+		}
 		switch (errno) {
-		case EWOULDBLOCK:
+		case EAGAIN:
 			/* Value already changed. */
 			goto end;
 		case EINTR:
 			/* Retry if interrupted by signal. */
-			break;	/* Get out of switch. */
+			break;	/* Get out of switch. Check again. */
 		default:
 			/* Unexpected error. */
 			urcu_die(errno);
@@ -441,7 +453,7 @@ void synchronize_rcu(void)
 	/*
 	 * Wait for readers to observe original parity or be quiescent.
 	 * wait_for_readers() can release and grab again rcu_registry_lock
-	 * interally.
+	 * internally.
 	 */
 	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 
@@ -483,7 +495,7 @@ void synchronize_rcu(void)
 	/*
 	 * Wait for readers to observe new parity or be quiescent.
 	 * wait_for_readers() can release and grab again rcu_registry_lock
-	 * interally.
+	 * internally.
 	 */
 	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 
@@ -529,14 +541,58 @@ int rcu_read_ongoing(void)
 	return _rcu_read_ongoing();
 }
 
+#ifdef RCU_SIGNAL
+/*
+ * Make sure the signal used by the urcu-signal flavor is unblocked
+ * while the thread is registered.
+ */
+static
+void urcu_signal_unblock(void)
+{
+	sigset_t mask, oldmask;
+	int ret;
+
+	ret = sigemptyset(&mask);
+	urcu_posix_assert(!ret);
+	ret = sigaddset(&mask, SIGRCU);
+	urcu_posix_assert(!ret);
+	ret = pthread_sigmask(SIG_UNBLOCK, &mask, &oldmask);
+	urcu_posix_assert(!ret);
+	URCU_TLS(rcu_signal_was_blocked) = sigismember(&oldmask, SIGRCU);
+}
+
+static
+void urcu_signal_restore(void)
+{
+	sigset_t mask;
+	int ret;
+
+	if (!URCU_TLS(rcu_signal_was_blocked))
+		return;
+	ret = sigemptyset(&mask);
+	urcu_posix_assert(!ret);
+	ret = sigaddset(&mask, SIGRCU);
+	urcu_posix_assert(!ret);
+	ret = pthread_sigmask(SIG_BLOCK, &mask, NULL);
+	urcu_posix_assert(!ret);
+}
+#else
+static
+void urcu_signal_unblock(void) { }
+static
+void urcu_signal_restore(void) { }
+#endif
+
 void rcu_register_thread(void)
 {
+	urcu_signal_unblock();
+
 	URCU_TLS(rcu_reader).tid = pthread_self();
-	assert(URCU_TLS(rcu_reader).need_mb == 0);
-	assert(!(URCU_TLS(rcu_reader).ctr & URCU_GP_CTR_NEST_MASK));
+	urcu_posix_assert(URCU_TLS(rcu_reader).need_mb == 0);
+	urcu_posix_assert(!(URCU_TLS(rcu_reader).ctr & URCU_GP_CTR_NEST_MASK));
 
 	mutex_lock(&rcu_registry_lock);
-	assert(!URCU_TLS(rcu_reader).registered);
+	urcu_posix_assert(!URCU_TLS(rcu_reader).registered);
 	URCU_TLS(rcu_reader).registered = 1;
 	rcu_init();	/* In case gcc does not support constructor attribute */
 	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
@@ -546,10 +602,12 @@ void rcu_register_thread(void)
 void rcu_unregister_thread(void)
 {
 	mutex_lock(&rcu_registry_lock);
-	assert(URCU_TLS(rcu_reader).registered);
+	urcu_posix_assert(URCU_TLS(rcu_reader).registered);
 	URCU_TLS(rcu_reader).registered = 0;
 	cds_list_del(&URCU_TLS(rcu_reader).node);
 	mutex_unlock(&rcu_registry_lock);
+
+	urcu_signal_restore();
 }
 
 #ifdef RCU_MEMBARRIER
@@ -640,21 +698,24 @@ void rcu_init(void)
 		urcu_die(errno);
 }
 
+/*
+ * Don't unregister the SIGRCU signal handler anymore, because
+ * call_rcu threads could still be using it shortly before the
+ * application exits.
+ * Assertion disabled because call_rcu threads are now rcu
+ * readers, and left running at exit.
+ * urcu_posix_assert(cds_list_empty(&registry));
+ */
+
+#endif /* #ifdef RCU_SIGNAL */
+
 void rcu_exit(void)
 {
-	/*
-	 * Don't unregister the SIGRCU signal handler anymore, because
-	 * call_rcu threads could still be using it shortly before the
-	 * application exits.
-	 * Assertion disabled because call_rcu threads are now rcu
-	 * readers, and left running at exit.
-	 * assert(cds_list_empty(&registry));
-	 */
+	urcu_call_rcu_exit();
 }
 
-#endif /* #ifdef RCU_SIGNAL */
-
 DEFINE_RCU_FLAVOR(rcu_flavor);
 
 #include "urcu-call-rcu-impl.h"
 #include "urcu-defer-impl.h"
+#include "urcu-poll-impl.h"