urcu call_rcu: Use RCU read-side protection for per-cpu call_rcu data

[urcu.git] / urcu-call-rcu-impl.h

diff --git a/urcu-call-rcu-impl.h b/urcu-call-rcu-impl.h
index 0a47d969a4e8d3f50438fc69bbede379e6715c50..d09adb1bc431a55923d3bbeb3904939f3344e460 100644 (file)
--- a/urcu-call-rcu-impl.h
+++ b/urcu-call-rcu-impl.h
@@ -82,7 +82,10 @@ 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;
@@ -109,7 +112,7 @@ 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");
@@ -330,13 +333,18 @@ 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");
@@ -344,7 +352,7 @@ 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]);
 }
 
 /*
@@ -418,7 +426,7 @@ int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
                return -EEXIST;
        }
 
-       per_cpu_call_rcu_data[cpu] = crdp;
+       rcu_set_pointer(&per_cpu_call_rcu_data[cpu], crdp);
        call_rcu_unlock(&call_rcu_mutex);
        return 0;
 }
@@ -450,6 +458,9 @@ 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)
 {
@@ -564,6 +575,8 @@ 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,
@@ -573,10 +586,13 @@ 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();
 }
 
 /*
@@ -641,17 +657,37 @@ 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;
+       }
+
        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);
 }
 
 /*
@@ -700,7 +736,7 @@ void call_rcu_after_fork_child(void)
        /* Cleanup call_rcu_data pointers before use */
        maxcpus_reset();
        free(per_cpu_call_rcu_data);
-       per_cpu_call_rcu_data = NULL;
+       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. */