1 files changed, 24 insertions, 5 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 4d2c068ba13e..d9d7a89da8bb 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -68,6 +68,7 @@ struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
 DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
 static struct rcu_state *rcu_state = &rcu_preempt_state;
 
+static void rcu_read_unlock_special(struct task_struct *t);
 static int rcu_preempted_readers_exp(struct rcu_node *rnp);
 
 /*
@@ -147,7 +148,7 @@ static void rcu_preempt_note_context_switch(int cpu)
         struct rcu_data *rdp;
         struct rcu_node *rnp;
 
-        if (t->rcu_read_lock_nesting &&
+        if (t->rcu_read_lock_nesting > 0 &&
             (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
 
                 /* Possibly blocking in an RCU read-side critical section. */
@@ -190,6 +191,14 @@ static void rcu_preempt_note_context_switch(int cpu)
                                 rnp->gp_tasks = &t->rcu_node_entry;
                 }
                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
+        } else if (t->rcu_read_lock_nesting < 0 &&
+                   t->rcu_read_unlock_special) {
+
+                /*
+                 * Complete exit from RCU read-side critical section on
+                 * behalf of preempted instance of __rcu_read_unlock().
+                 */
+                rcu_read_unlock_special(t);
         }
 
         /*
@@ -391,13 +400,22 @@ void __rcu_read_unlock(void)
         struct task_struct *t = current;
 
         barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
-        if (--t->rcu_read_lock_nesting == 0) {
-                barrier();  /* decr before ->rcu_read_unlock_special load */
+        if (t->rcu_read_lock_nesting != 1)
+                --t->rcu_read_lock_nesting;
+        else {
+                t->rcu_read_lock_nesting = INT_MIN;
+                barrier();  /* assign before ->rcu_read_unlock_special load */
                 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
                         rcu_read_unlock_special(t);
+                barrier();  /* ->rcu_read_unlock_special load before assign */
+                t->rcu_read_lock_nesting = 0;
         }
 #ifdef CONFIG_PROVE_LOCKING
-        WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
+        {
+                int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
+
+                WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
+        }
 #endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
@@ -593,7 +611,8 @@ static void rcu_preempt_check_callbacks(int cpu)
                 rcu_preempt_qs(cpu);
                 return;
         }
-        if (per_cpu(rcu_preempt_data, cpu).qs_pending)
+        if (t->rcu_read_lock_nesting > 0 &&
+            per_cpu(rcu_preempt_data, cpu).qs_pending)
                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 }