linux-kernel - [PATCH 10/16] rcu: Check for RCU_FLAG_GP_INIT bit in gp

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Date:	Wed, 23 Jul 2014 01:09:47 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	linux-kernel@...r.kernel.org (open list:READ-COPY UPDATE...)
Subject: [PATCH 10/16] rcu: Check for RCU_FLAG_GP_INIT bit in gp_flags for spurious wakeup

rcu_gp_init() is called once the gp_kthread wakes up on the condition that
the init bit is set in the gp_flags. For a spurious wakeup we need to check that
it is actually set. This commit ensures that the RCU_GP_FLAG_INIT bit is set in
gp_flags.

Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8d598a2..f8847d9 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1600,7 +1600,7 @@ static int rcu_gp_init(struct rcu_state *rsp)
 	rcu_bind_gp_kthread();
 	raw_spin_lock_irq(&rnp->lock);
 	smp_mb__after_unlock_lock();
-	if (!ACCESS_ONCE(rsp->gp_flags)) {
+	if (!(ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_INIT)) {
 		/* Spurious wakeup, tell caller to go back to sleep.  */
 		raw_spin_unlock_irq(&rnp->lock);
 		return 0;
-- 
2.0.0.rc2

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