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>

1 files changed, 14 insertions, 1 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 32618b3fe4e6..1dc9f3604ad8 100644
--- 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)