X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=blobdiff_plain;f=urcu-call-rcu-impl.h;h=6ea7b9a05d74bdfb0c2760d426306d663cb0ade8;hp=e0a8fd883ee4a24782b3464a970f20be645b5fdc;hb=refs%2Fheads%2Fstable-0.6;hpb=f377678692caa9f589275eae4f2774104f26a8c6

diff --git a/urcu-call-rcu-impl.h b/urcu-call-rcu-impl.h
index e0a8fd8..6ea7b9a 100644
--- a/urcu-call-rcu-impl.h
+++ b/urcu-call-rcu-impl.h
@@ -64,8 +64,9 @@ CDS_LIST_HEAD(call_rcu_data_list);
 
 static __thread struct call_rcu_data *thread_call_rcu_data;
 
-/* Guard call_rcu thread creation. */
-
+/*
+ * Guard call_rcu thread creation and atfork handlers.
+ */
 static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 /* If a given thread does not have its own call_rcu thread, this is default. */
@@ -82,12 +83,20 @@ static struct call_rcu_data *default_call_rcu_data;
 
 /*
  * Pointer to array of pointers to per-CPU call_rcu_data structures
- * and # CPUs.
+ * and # CPUs. per_cpu_call_rcu_data is a RCU-protected pointer to an
+ * array of RCU-protected pointers to call_rcu_data. call_rcu acts as a
+ * RCU read-side and reads per_cpu_call_rcu_data and the per-cpu pointer
+ * without mutex. The call_rcu_mutex protects updates.
  */
 
 static struct call_rcu_data **per_cpu_call_rcu_data;
 static long maxcpus;
 
+static void maxcpus_reset(void)
+{
+	maxcpus = 0;
+}
+
 /* Allocate the array if it has not already been allocated. */
 
 static void alloc_cpu_call_rcu_data(void)
@@ -104,7 +113,7 @@ static void alloc_cpu_call_rcu_data(void)
 	p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
 	if (p != NULL) {
 		memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
-		per_cpu_call_rcu_data = p;
+		rcu_set_pointer(&per_cpu_call_rcu_data, p);
 	} else {
 		if (!warned) {
 			fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
@@ -123,6 +132,10 @@ static void alloc_cpu_call_rcu_data(void)
 static struct call_rcu_data **per_cpu_call_rcu_data = NULL;
 static const long maxcpus = -1;
 
+static void maxcpus_reset(void)
+{
+}
+
 static void alloc_cpu_call_rcu_data(void)
 {
 }
@@ -192,7 +205,7 @@ static void call_rcu_wake_up(struct call_rcu_data *crdp)
 {
 	/* Write to call_rcu list before reading/writing futex */
 	cmm_smp_mb();
-	if (unlikely(uatomic_read(&crdp->futex) == -1)) {
+	if (caa_unlikely(uatomic_read(&crdp->futex) == -1)) {
 		uatomic_set(&crdp->futex, 0);
 		futex_async(&crdp->futex, FUTEX_WAKE, 1,
 		      NULL, NULL, 0);
@@ -227,6 +240,21 @@ static void *call_rcu_thread(void *arg)
 		cmm_smp_mb();
 	}
 	for (;;) {
+		if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) {
+			/*
+			 * Pause requested. Become quiescent: remove
+			 * ourself from all global lists, and don't
+			 * process any callback. The callback lists may
+			 * still be non-empty though.
+			 */
+			rcu_unregister_thread();
+			cmm_smp_mb__before_uatomic_or();
+			uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSED);
+			while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) != 0)
+				poll(NULL, 0, 1);
+			rcu_register_thread();
+		}
+
 		if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 			while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
 				poll(NULL, 0, 1);
@@ -321,13 +349,18 @@ static void call_rcu_data_init(struct call_rcu_data **crdpp,
  * CPU, returning NULL if there is none.  We cannot automatically
  * created it because the platform we are running on might not define
  * sched_getcpu().
+ *
+ * The call to this function and use of the returned call_rcu_data
+ * should be protected by RCU read-side lock.
  */
 
 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
 {
 	static int warned = 0;
+	struct call_rcu_data **pcpu_crdp;
 
-	if (per_cpu_call_rcu_data == NULL)
+	pcpu_crdp = rcu_dereference(per_cpu_call_rcu_data);
+	if (pcpu_crdp == NULL)
 		return NULL;
 	if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
 		fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
@@ -335,7 +368,7 @@ struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
 	}
 	if (cpu < 0 || maxcpus <= cpu)
 		return NULL;
-	return per_cpu_call_rcu_data[cpu];
+	return rcu_dereference(pcpu_crdp[cpu]);
 }
 
 /*
@@ -379,6 +412,10 @@ struct call_rcu_data *create_call_rcu_data(unsigned long flags,
  * the caller's responsibility to dispose of the removed structure.
  * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
  * (prior to NULLing it out, of course).
+ *
+ * The caller must wait for a grace-period to pass between return from
+ * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
+ * previous call rcu data as argument.
  */
 
 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
@@ -396,12 +433,21 @@ int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
 		errno = EINVAL;
 		return -EINVAL;
 	}
-	call_rcu_unlock(&call_rcu_mutex);
+
 	if (per_cpu_call_rcu_data == NULL) {
+		call_rcu_unlock(&call_rcu_mutex);
 		errno = ENOMEM;
 		return -ENOMEM;
 	}
-	per_cpu_call_rcu_data[cpu] = crdp;
+
+	if (per_cpu_call_rcu_data[cpu] != NULL && crdp != NULL) {
+		call_rcu_unlock(&call_rcu_mutex);
+		errno = EEXIST;
+		return -EEXIST;
+	}
+
+	rcu_set_pointer(&per_cpu_call_rcu_data[cpu], crdp);
+	call_rcu_unlock(&call_rcu_mutex);
 	return 0;
 }
 
@@ -432,25 +478,23 @@ struct call_rcu_data *get_default_call_rcu_data(void)
  * structure assigned to the CPU on which the thread is running,
  * followed by the default call_rcu_data structure.  If there is not
  * yet a default call_rcu_data structure, one will be created.
+ *
+ * Calls to this function and use of the returned call_rcu_data should
+ * be protected by RCU read-side lock.
  */
 struct call_rcu_data *get_call_rcu_data(void)
 {
-	int curcpu;
-	static int warned = 0;
+	struct call_rcu_data *crd;
 
 	if (thread_call_rcu_data != NULL)
 		return thread_call_rcu_data;
-	if (maxcpus <= 0)
-		return get_default_call_rcu_data();
-	curcpu = sched_getcpu();
-	if (!warned && (curcpu < 0 || maxcpus <= curcpu)) {
-		fprintf(stderr, "[error] liburcu: gcrd CPU # out of range\n");
-		warned = 1;
+
+	if (maxcpus > 0) {
+		crd = get_cpu_call_rcu_data(sched_getcpu());
+		if (crd)
+			return crd;
 	}
-	if (curcpu >= 0 && maxcpus > curcpu &&
-	    per_cpu_call_rcu_data != NULL &&
-	    per_cpu_call_rcu_data[curcpu] != NULL)
-	    	return per_cpu_call_rcu_data[curcpu];
+
 	return get_default_call_rcu_data();
 }
 
@@ -518,8 +562,13 @@ int create_all_cpu_call_rcu_data(unsigned long flags)
 		}
 		call_rcu_unlock(&call_rcu_mutex);
 		if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
-			/* FIXME: Leaks crdp for now. */
-			return ret; /* Can happen on race. */
+			call_rcu_data_free(crdp);
+
+			/* it has been created by other thread */
+			if (ret == -EEXIST)
+				continue;
+
+			return ret;
 		}
 	}
 	return 0;
@@ -546,6 +595,8 @@ static void wake_call_rcu_thread(struct call_rcu_data *crdp)
  * need the first invocation of call_rcu() to be fast, make sure
  * to create a call_rcu thread first.  One way to accomplish this is
  * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
+ *
+ * call_rcu must be called by registered RCU read-side threads.
  */
 
 void call_rcu(struct rcu_head *head,
@@ -555,10 +606,13 @@ void call_rcu(struct rcu_head *head,
 
 	cds_wfq_node_init(&head->next);
 	head->func = func;
+	/* Holding rcu read-side lock across use of per-cpu crdp */
+	rcu_read_lock();
 	crdp = get_call_rcu_data();
 	cds_wfq_enqueue(&crdp->cbs, &head->next);
 	uatomic_inc(&crdp->qlen);
 	wake_call_rcu_thread(crdp);
+	rcu_read_unlock();
 }
 
 /*
@@ -578,6 +632,10 @@ void call_rcu(struct rcu_head *head,
  *
  * We also silently refuse to free NULL pointers.  This simplifies
  * the calling code.
+ *
+ * The caller must wait for a grace-period to pass between return from
+ * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
+ * previous call rcu data as argument.
  */
 void call_rcu_data_free(struct call_rcu_data *crdp)
 {
@@ -600,14 +658,22 @@ void call_rcu_data_free(struct call_rcu_data *crdp)
 		_CMM_STORE_SHARED(crdp->cbs.head, NULL);
 		cbs_tail = (struct cds_wfq_node **)
 			uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
+		/* Create default call rcu data if need be */
+		(void) get_default_call_rcu_data();
 		cbs_endprev = (struct cds_wfq_node **)
-			uatomic_xchg(&default_call_rcu_data, cbs_tail);
-		*cbs_endprev = cbs;
+			uatomic_xchg(&default_call_rcu_data->cbs.tail,
+					cbs_tail);
+		_CMM_STORE_SHARED(*cbs_endprev, cbs);
 		uatomic_add(&default_call_rcu_data->qlen,
 			    uatomic_read(&crdp->qlen));
-		cds_list_del(&crdp->list);
-		free(crdp);
+		wake_call_rcu_thread(default_call_rcu_data);
 	}
+
+	call_rcu_lock(&call_rcu_mutex);
+	cds_list_del(&crdp->list);
+	call_rcu_unlock(&call_rcu_mutex);
+
+	free(crdp);
 }
 
 /*
@@ -616,27 +682,61 @@ void call_rcu_data_free(struct call_rcu_data *crdp)
 void free_all_cpu_call_rcu_data(void)
 {
 	int cpu;
-	struct call_rcu_data *crdp;
+	struct call_rcu_data **crdp;
+	static int warned = 0;
 
 	if (maxcpus <= 0)
 		return;
+
+	crdp = malloc(sizeof(*crdp) * maxcpus);
+	if (!crdp) {
+		if (!warned) {
+			fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
+		}
+		warned = 1;
+		return;
+	}
+
 	for (cpu = 0; cpu < maxcpus; cpu++) {
-		crdp = get_cpu_call_rcu_data(cpu);
-		if (crdp == NULL)
+		crdp[cpu] = get_cpu_call_rcu_data(cpu);
+		if (crdp[cpu] == NULL)
 			continue;
 		set_cpu_call_rcu_data(cpu, NULL);
-		call_rcu_data_free(crdp);
 	}
+	/*
+	 * Wait for call_rcu sites acting as RCU readers of the
+	 * call_rcu_data to become quiescent.
+	 */
+	synchronize_rcu();
+	for (cpu = 0; cpu < maxcpus; cpu++) {
+		if (crdp[cpu] == NULL)
+			continue;
+		call_rcu_data_free(crdp[cpu]);
+	}
+	free(crdp);
 }
 
 /*
  * Acquire the call_rcu_mutex in order to ensure that the child sees
- * all of the call_rcu() data structures in a consistent state.
+ * all of the call_rcu() data structures in a consistent state. Ensure
+ * that all call_rcu threads are in a quiescent state across fork.
  * Suitable for pthread_atfork() and friends.
  */
 void call_rcu_before_fork(void)
 {
+	struct call_rcu_data *crdp;
+
 	call_rcu_lock(&call_rcu_mutex);
+
+	cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
+		uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSE);
+		cmm_smp_mb__after_uatomic_or();
+		wake_call_rcu_thread(crdp);
+	}
+	cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
+		while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) == 0)
+			poll(NULL, 0, 1);
+	}
 }
 
 /*
@@ -646,6 +746,10 @@ void call_rcu_before_fork(void)
  */
 void call_rcu_after_fork_parent(void)
 {
+	struct call_rcu_data *crdp;
+
+	cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
+		uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSE);
 	call_rcu_unlock(&call_rcu_mutex);
 }
 
@@ -656,11 +760,15 @@ void call_rcu_after_fork_parent(void)
  */
 void call_rcu_after_fork_child(void)
 {
-	struct call_rcu_data *crdp;
+	struct call_rcu_data *crdp, *next;
 
 	/* Release the mutex. */
 	call_rcu_unlock(&call_rcu_mutex);
 
+	/* Do nothing when call_rcu() has not been used */
+	if (cds_list_empty(&call_rcu_data_list))
+		return;
+
 	/*
 	 * Allocate a new default call_rcu_data structure in order
 	 * to get a working call_rcu thread to go with it.
@@ -668,13 +776,20 @@ void call_rcu_after_fork_child(void)
 	default_call_rcu_data = NULL;
 	(void)get_default_call_rcu_data();
 
-	/* Dispose of all of the rest of the call_rcu_data structures. */
-	while (call_rcu_data_list.next != call_rcu_data_list.prev) {
-		crdp = cds_list_entry(call_rcu_data_list.prev,
-				      struct call_rcu_data, list);
+	/* Cleanup call_rcu_data pointers before use */
+	maxcpus_reset();
+	free(per_cpu_call_rcu_data);
+	rcu_set_pointer(&per_cpu_call_rcu_data, NULL);
+	thread_call_rcu_data = NULL;
+
+	/*
+	 * Dispose of all of the rest of the call_rcu_data structures.
+	 * Leftover call_rcu callbacks will be merged into the new
+	 * default call_rcu thread queue.
+	 */
+	cds_list_for_each_entry_safe(crdp, next, &call_rcu_data_list, list) {
 		if (crdp == default_call_rcu_data)
-			crdp = cds_list_entry(crdp->list.prev,
-					      struct call_rcu_data, list);
+			continue;
 		uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
 		call_rcu_data_free(crdp);
 	}