linux-kernel - [PATCH RFC tip/core/rcu 02/18] rcu: adjust force_quiescent

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Date:	Tue, 15 Dec 2009 15:02:25 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH RFC tip/core/rcu 02/18] rcu: adjust force_quiescent_state() locking, step 2

From: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Proposed for 2.6.34, not for inclusion.

This patch releases rnp->lock after the end of force_quiescent_state()'s
switch statement.  This is a second step towards prohibiting starting
grace periods while force_quiescent_state() is executing, which will
reduce the number and complexity of races that force_quiescent_state()
is involved in.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree.c |   13 +++----------
 1 files changed, 3 insertions(+), 10 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index eae331d..d42ad30 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1219,7 +1219,6 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 	case RCU_GP_IDLE:
 	case RCU_GP_INIT:
 
-		spin_unlock(&rnp->lock);
 		break; /* grace period idle or initializing, ignore. */
 
 	case RCU_SAVE_DYNTICK:
@@ -1246,10 +1245,8 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 			rsp->completed_fqs = lastcomp;
 			forcenow = signaled == RCU_SAVE_COMPLETED;
 		}
-		if (!forcenow) {
-			spin_unlock(&rnp->lock);
+		if (!forcenow)
 			break;
-		}
 		/* fall into next case. */
 
 	case RCU_FORCE_QS:
@@ -1262,14 +1259,10 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 
 		/* Leave state in case more forcing is required. */
 
-		break;
-
-	default:
-
-		spin_unlock(&rnp->lock);
-		WARN_ON_ONCE(1);
+		spin_lock(&rnp->lock);
 		break;
 	}
+	spin_unlock(&rnp->lock);
 unlock_fqs_ret:
 	spin_unlock_irqrestore(&rsp->fqslock, flags);
 }
-- 
1.5.2.5

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