[tip:core/rcu] rcu: Adjust force_quiescent_state() locking, step 2

["tip-bot for Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

Commit-ID:  559569acf94f538b56bd6eead80b439d6a78cdff
Gitweb:     http://git.kernel.org/tip/559569acf94f538b56bd6eead80b439d6a78cdff
Author:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Mon, 4 Jan 2010 15:09:01 -0800
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 13 Jan 2010 09:06:01 +0100

rcu: Adjust force_quiescent_state() locking, step 2

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@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626465501994-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 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);
 }