5 files changed, 186 insertions, 15 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 0cdfdb622faa..3c89d6a2591f 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -51,7 +51,19 @@ struct rcu_head {
         void (*func)(struct rcu_head *head);
 };
 
-/* Internal to kernel, but needed by rcupreempt.h. */
+/* Exported common interfaces */
+extern void synchronize_rcu(void);
+extern void synchronize_rcu_bh(void);
+extern void rcu_barrier(void);
+extern void rcu_barrier_bh(void);
+extern void rcu_barrier_sched(void);
+extern void synchronize_sched_expedited(void);
+extern int sched_expedited_torture_stats(char *page);
+
+/* Internal to kernel */
+extern void rcu_init(void);
+extern void rcu_scheduler_starting(void);
+extern int rcu_needs_cpu(int cpu);
 extern int rcu_scheduler_active;
 
 #if defined(CONFIG_TREE_RCU)
@@ -257,15 +269,4 @@ extern void call_rcu(struct rcu_head *head,
 extern void call_rcu_bh(struct rcu_head *head,
                         void (*func)(struct rcu_head *head));
 
-/* Exported common interfaces */
-extern void synchronize_rcu(void);
-extern void rcu_barrier(void);
-extern void rcu_barrier_bh(void);
-extern void rcu_barrier_sched(void);
-
-/* Internal to kernel */
-extern void rcu_init(void);
-extern void rcu_scheduler_starting(void);
-extern int rcu_needs_cpu(int cpu);
-
 #endif /* __LINUX_RCUPDATE_H */
diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h
index fce522782ffa..f164ac9b7807 100644
--- a/include/linux/rcupreempt.h
+++ b/include/linux/rcupreempt.h
@@ -74,6 +74,16 @@ extern int rcu_needs_cpu(int cpu);
 
 extern void __synchronize_sched(void);
 
+static inline void synchronize_rcu_expedited(void)
+{
+        synchronize_rcu();  /* Placeholder for new rcupreempt implementation. */
+}
+
+static inline void synchronize_rcu_bh_expedited(void)
+{
+        synchronize_rcu_bh();  /* Placeholder for new rcupreempt impl. */
+}
+
 extern void __rcu_init(void);
 extern void rcu_init_sched(void);
 extern void rcu_check_callbacks(int cpu, int user);
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 5a5153806c42..d4dfd2489633 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -286,8 +286,14 @@ static inline void __rcu_read_unlock_bh(void)
 
 #define call_rcu_sched(head, func) call_rcu(head, func)
 
-static inline void rcu_init_sched(void)
+static inline void synchronize_rcu_expedited(void)
+{
+        synchronize_sched_expedited();
+}
+
+static inline void synchronize_rcu_bh_expedited(void)
 {
+        synchronize_sched_expedited();
 }
 
 extern void __rcu_init(void);
@@ -297,6 +303,10 @@ extern void rcu_restart_cpu(int cpu);
 extern long rcu_batches_completed(void);
 extern long rcu_batches_completed_bh(void);
 
+static inline void rcu_init_sched(void)
+{
+}
+
 #ifdef CONFIG_NO_HZ
 void rcu_enter_nohz(void);
 void rcu_exit_nohz(void);
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index a967c9feb90a..eae29c25fb14 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -98,6 +98,30 @@ void synchronize_rcu(void)
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu);
 
+/**
+ * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full rcu_bh grace
+ * period has elapsed, in other words after all currently executing rcu_bh
+ * read-side critical sections have completed.  RCU read-side critical
+ * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
+ * and may be nested.
+ */
+void synchronize_rcu_bh(void)
+{
+        struct rcu_synchronize rcu;
+
+        if (rcu_blocking_is_gp())
+                return;
+
+        init_completion(&rcu.completion);
+        /* Will wake me after RCU finished. */
+        call_rcu_bh(&rcu.head, wakeme_after_rcu);
+        /* Wait for it. */
+        wait_for_completion(&rcu.completion);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
+
 static void rcu_barrier_callback(struct rcu_head *notused)
 {
         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
@@ -129,6 +153,7 @@ static void rcu_barrier_func(void *type)
 static inline void wait_migrated_callbacks(void)
 {
         wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
+        smp_mb(); /* In case we didn't sleep. */
 }
 
 /*
diff --git a/kernel/sched.c b/kernel/sched.c
index 7c9098d186e6..9ae80bec1c1e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7024,6 +7024,11 @@ fail:
         return ret;
 }
 
+#define RCU_MIGRATION_IDLE      0
+#define RCU_MIGRATION_NEED_QS   1
+#define RCU_MIGRATION_GOT_QS    2
+#define RCU_MIGRATION_MUST_SYNC 3
+
 /*
  * migration_thread - this is a highprio system thread that performs
  * thread migration by bumping thread off CPU then 'pushing' onto
@@ -7031,6 +7036,7 @@ fail:
  */
 static int migration_thread(void *data)
 {
+        int badcpu;
         int cpu = (long)data;
         struct rq *rq;
 
@@ -7065,8 +7071,17 @@ static int migration_thread(void *data)
                 req = list_entry(head->next, struct migration_req, list);
                 list_del_init(head->next);
 
-                spin_unlock(&rq->lock);
-                __migrate_task(req->task, cpu, req->dest_cpu);
+                if (req->task != NULL) {
+                        spin_unlock(&rq->lock);
+                        __migrate_task(req->task, cpu, req->dest_cpu);
+                } else if (likely(cpu == (badcpu = smp_processor_id()))) {
+                        req->dest_cpu = RCU_MIGRATION_GOT_QS;
+                        spin_unlock(&rq->lock);
+                } else {
+                        req->dest_cpu = RCU_MIGRATION_MUST_SYNC;
+                        spin_unlock(&rq->lock);
+                        WARN_ONCE(1, "migration_thread() on CPU %d, expected %d\n", badcpu, cpu);
+                }
                 local_irq_enable();
 
                 complete(&req->done);
@@ -10554,3 +10569,113 @@ struct cgroup_subsys cpuacct_subsys = {
         .subsys_id = cpuacct_subsys_id,
 };
 #endif  /* CONFIG_CGROUP_CPUACCT */
+
+#ifndef CONFIG_SMP
+
+int rcu_expedited_torture_stats(char *page)
+{
+        return 0;
+}
+EXPORT_SYMBOL_GPL(rcu_expedited_torture_stats);
+
+void synchronize_sched_expedited(void)
+{
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+#else /* #ifndef CONFIG_SMP */
+
+static DEFINE_PER_CPU(struct migration_req, rcu_migration_req);
+static DEFINE_MUTEX(rcu_sched_expedited_mutex);
+
+#define RCU_EXPEDITED_STATE_POST -2
+#define RCU_EXPEDITED_STATE_IDLE -1
+
+static int rcu_expedited_state = RCU_EXPEDITED_STATE_IDLE;
+
+int rcu_expedited_torture_stats(char *page)
+{
+        int cnt = 0;
+        int cpu;
+
+        cnt += sprintf(&page[cnt], "state: %d /", rcu_expedited_state);
+        for_each_online_cpu(cpu) {
+                 cnt += sprintf(&page[cnt], " %d:%d",
+                                cpu, per_cpu(rcu_migration_req, cpu).dest_cpu);
+        }
+        cnt += sprintf(&page[cnt], "\n");
+        return cnt;
+}
+EXPORT_SYMBOL_GPL(rcu_expedited_torture_stats);
+
+static long synchronize_sched_expedited_count;
+
+/*
+ * Wait for an rcu-sched grace period to elapse, but use "big hammer"
+ * approach to force grace period to end quickly.  This consumes
+ * significant time on all CPUs, and is thus not recommended for
+ * any sort of common-case code.
+ *
+ * Note that it is illegal to call this function while holding any
+ * lock that is acquired by a CPU-hotplug notifier.  Failing to
+ * observe this restriction will result in deadlock.
+ */
+void synchronize_sched_expedited(void)
+{
+        int cpu;
+        unsigned long flags;
+        bool need_full_sync = 0;
+        struct rq *rq;
+        struct migration_req *req;
+        long snap;
+        int trycount = 0;
+
+        smp_mb();  /* ensure prior mod happens before capturing snap. */
+        snap = ACCESS_ONCE(synchronize_sched_expedited_count) + 1;
+        get_online_cpus();
+        while (!mutex_trylock(&rcu_sched_expedited_mutex)) {
+                put_online_cpus();
+                if (trycount++ < 10)
+                        udelay(trycount * num_online_cpus());
+                else {
+                        synchronize_sched();
+                        return;
+                }
+                if (ACCESS_ONCE(synchronize_sched_expedited_count) - snap > 0) {
+                        smp_mb(); /* ensure test happens before caller kfree */
+                        return;
+                }
+                get_online_cpus();
+        }
+        rcu_expedited_state = RCU_EXPEDITED_STATE_POST;
+        for_each_online_cpu(cpu) {
+                rq = cpu_rq(cpu);
+                req = &per_cpu(rcu_migration_req, cpu);
+                init_completion(&req->done);
+                req->task = NULL;
+                req->dest_cpu = RCU_MIGRATION_NEED_QS;
+                spin_lock_irqsave(&rq->lock, flags);
+                list_add(&req->list, &rq->migration_queue);
+                spin_unlock_irqrestore(&rq->lock, flags);
+                wake_up_process(rq->migration_thread);
+        }
+        for_each_online_cpu(cpu) {
+                rcu_expedited_state = cpu;
+                req = &per_cpu(rcu_migration_req, cpu);
+                rq = cpu_rq(cpu);
+                wait_for_completion(&req->done);
+                spin_lock_irqsave(&rq->lock, flags);
+                if (unlikely(req->dest_cpu == RCU_MIGRATION_MUST_SYNC))
+                        need_full_sync = 1;
+                req->dest_cpu = RCU_MIGRATION_IDLE;
+                spin_unlock_irqrestore(&rq->lock, flags);
+        }
+        rcu_expedited_state = RCU_EXPEDITED_STATE_IDLE;
+        mutex_unlock(&rcu_sched_expedited_mutex);
+        put_online_cpus();
+        if (need_full_sync)
+                synchronize_sched();
+}
+EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+#endif /* #else #ifndef CONFIG_SMP */