Disable signals in URCU background threads

[urcu.git] / src / urcu.c

diff --git a/src/urcu.c b/src/urcu.c
index 902b8f839a75b4df7e0b077ed780a2f0b0c4a433..cf4d6d03f711750c05e91991f2a64687640b4438 100644 (file)
--- 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>
@@ -110,6 +110,8 @@ 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
 
 /*
@@ -259,17 +261,25 @@ 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);
@@ -529,14 +539,58 @@ 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 +600,12 @@ 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
@@ -648,7 +704,7 @@ void rcu_exit(void)
         * application exits.
         * Assertion disabled because call_rcu threads are now rcu
         * readers, and left running at exit.
-        * assert(cds_list_empty(&registry));
+        * urcu_posix_assert(cds_list_empty(&registry));
         */
 }