sched, rcu: Make RCU use resched_cpu()

We're going to deprecate and remove set_need_resched() for it will do
the wrong thing. Make an exception for RCU and allow it to use
resched_cpu() which will do the right thing.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-2eywnacjl1nllctl1nszqa5w@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 32618b3fe4e6aa375b3cd3bde1acd12bdd4237b3..1dc9f3604ad8eef54ed409f685e362f12cfc7331 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -898,6 +898,12 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
        force_quiescent_state(rsp);  /* Kick them all. */
 }
 
+/*
+ * This function really isn't for public consumption, but RCU is special in
+ * that context switches can allow the state machine to make progress.
+ */
+extern void resched_cpu(int cpu);
+
 static void print_cpu_stall(struct rcu_state *rsp)
 {
        int cpu;
@@ -927,7 +933,14 @@ static void print_cpu_stall(struct rcu_state *rsp)
                                     3 * rcu_jiffies_till_stall_check() + 3;
        raw_spin_unlock_irqrestore(&rnp->lock, flags);
 
-       set_need_resched();  /* kick ourselves to get things going. */
+       /*
+        * Attempt to revive the RCU machinery by forcing a context switch.
+        *
+        * A context switch would normally allow the RCU state machine to make
+        * progress and it could be we're stuck in kernel space without context
+        * switches for an entirely unreasonable amount of time.
+        */
+       resched_cpu(smp_processor_id());
 }
 
 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ac5796783c498055849c0c1d38b2e4d2246555a0..242da0c03aba586473ff0568d83c194c952aaead 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -513,12 +513,11 @@ static inline void init_hrtick(void)
  * might also involve a cross-CPU call to trigger the scheduler on
  * the target CPU.
  */
-#ifdef CONFIG_SMP
 void resched_task(struct task_struct *p)
 {
        int cpu;
 
-       assert_raw_spin_locked(&task_rq(p)->lock);
+       lockdep_assert_held(&task_rq(p)->lock);
 
        if (test_tsk_need_resched(p))
                return;
@@ -546,6 +545,7 @@ void resched_cpu(int cpu)
        raw_spin_unlock_irqrestore(&rq->lock, flags);
 }
 
+#ifdef CONFIG_SMP
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * In the semi idle case, use the nearest busy cpu for migrating timers
@@ -693,12 +693,6 @@ void sched_avg_update(struct rq *rq)
        }
 }
 
-#else /* !CONFIG_SMP */
-void resched_task(struct task_struct *p)
-{
-       assert_raw_spin_locked(&task_rq(p)->lock);
-       set_tsk_need_resched(p);
-}
 #endif /* CONFIG_SMP */
 
 #if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \