linux-kernel - [PATCH 11/16] rcu: Check for spurious wakeup using return value

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Date:	Wed, 23 Jul 2014 01:09:48 -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 11/16] rcu: Check for spurious wakeup using return value

When the gp_kthread wakes up from the wait event, it returns 0 if the wake up is
due to the condition having been met. This commit checks this return value
for a spurious wake up before calling rcu_gp_init().

Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
---
 kernel/rcu/tree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f8847d9..3b20ad2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1790,11 +1790,11 @@ static int __noreturn rcu_gp_kthread(void *arg)
 					       ACCESS_ONCE(rsp->gpnum),
 					       TPS("reqwait"));
 			rsp->gp_state = RCU_GP_WAIT_GPS;
-			wait_event_interruptible(rsp->gp_wq,
+			ret = wait_event_interruptible(rsp->gp_wq,
 						 ACCESS_ONCE(rsp->gp_flags) &
 						 RCU_GP_FLAG_INIT);
 			/* Locking provides needed memory barrier. */
-			if (rcu_gp_init(rsp))
+			if (!ret && rcu_gp_init(rsp))
 				break;
 			cond_resched();
 			flush_signals(current);
-- 
2.0.0.rc2

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