1 files changed, 47 insertions, 33 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 67fe75725486..f79a1c646846 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3309,16 +3309,6 @@ static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
         return rcu_seq_done(&rsp->expedited_sequence, s);
 }
 
-static int synchronize_sched_expedited_cpu_stop(void *data)
-{
-        struct rcu_state *rsp = data;
-
-        /* We are here: If we are last, do the wakeup. */
-        if (atomic_dec_and_test(&rsp->expedited_need_qs))
-                wake_up(&rsp->expedited_wq);
-        return 0;
-}
-
 /* Common code for synchronize_sched_expedited() work-done checking. */
 static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp,
                               atomic_long_t *stat, unsigned long s)
@@ -3335,6 +3325,48 @@ static bool sync_sched_exp_wd(struct rcu_state *rsp, struct rcu_node *rnp,
         return false;
 }
 
+/*
+ * Funnel-lock acquisition for expedited grace periods.  Returns a
+ * pointer to the root rcu_node structure, or NULL if some other
+ * task did the expedited grace period for us.
+ */
+static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
+{
+        struct rcu_node *rnp0;
+        struct rcu_node *rnp1 = NULL;
+
+        /*
+         * Each pass through the following loop works its way
+         * up the rcu_node tree, returning if others have done the
+         * work or otherwise falls through holding the root rnp's
+         * ->exp_funnel_mutex.  The mapping from CPU to rcu_node structure
+         * can be inexact, as it is just promoting locality and is not
+         * strictly needed for correctness.
+         */
+        rnp0 = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
+        for (; rnp0 != NULL; rnp0 = rnp0->parent) {
+                if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone1, s))
+                        return NULL;
+                mutex_lock(&rnp0->exp_funnel_mutex);
+                if (rnp1)
+                        mutex_unlock(&rnp1->exp_funnel_mutex);
+                rnp1 = rnp0;
+        }
+        if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone2, s))
+                return NULL;
+        return rnp1;
+}
+
+static int synchronize_sched_expedited_cpu_stop(void *data)
+{
+        struct rcu_state *rsp = data;
+
+        /* We are here: If we are last, do the wakeup. */
+        if (atomic_dec_and_test(&rsp->expedited_need_qs))
+                wake_up(&rsp->expedited_wq);
+        return 0;
+}
+
 /**
  * synchronize_sched_expedited - Brute-force RCU-sched grace period
  *
@@ -3355,8 +3387,7 @@ void synchronize_sched_expedited(void)
 {
         int cpu;
         long s;
-        struct rcu_node *rnp0;
-        struct rcu_node *rnp1 = NULL;
+        struct rcu_node *rnp;
         struct rcu_state *rsp = &rcu_sched_state;
 
         /* Take a snapshot of the sequence number.  */
@@ -3370,26 +3401,9 @@ void synchronize_sched_expedited(void)
         }
         WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
 
-        /*
-         * Each pass through the following loop works its way
-         * up the rcu_node tree, returning if others have done the
-         * work or otherwise falls through holding the root rnp's
-         * ->exp_funnel_mutex.  The mapping from CPU to rcu_node structure
-         * can be inexact, as it is just promoting locality and is not
-         * strictly needed for correctness.
-         */
-        rnp0 = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
-        for (; rnp0 != NULL; rnp0 = rnp0->parent) {
-                if (sync_sched_exp_wd(rsp, rnp1, &rsp->expedited_workdone1, s))
-                        return;
-                mutex_lock(&rnp0->exp_funnel_mutex);
-                if (rnp1)
-                        mutex_unlock(&rnp1->exp_funnel_mutex);
-                rnp1 = rnp0;
-        }
-        rnp0 = rnp1;  /* rcu_get_root(rsp), AKA root rcu_node structure. */
-        if (sync_sched_exp_wd(rsp, rnp0, &rsp->expedited_workdone2, s))
-                return;
+        rnp = exp_funnel_lock(rsp, s);
+        if (rnp == NULL)
+                return;  /* Someone else did our work for us. */
 
         rcu_exp_gp_seq_start(rsp);
 
@@ -3415,7 +3429,7 @@ void synchronize_sched_expedited(void)
                            !atomic_read(&rsp->expedited_need_qs));
 
         rcu_exp_gp_seq_end(rsp);
-        mutex_unlock(&rnp0->exp_funnel_mutex);
+        mutex_unlock(&rnp->exp_funnel_mutex);
         smp_mb(); /* ensure subsequent action seen after grace period. */
 
         put_online_cpus();