linux-kernel - [PATCH tip/core/rcu 1/2] rcu: further cleanups of use of lastcomp

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Date:	Fri, 13 Nov 2009 19:51:38 -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 tip/core/rcu 1/2] rcu: further cleanups of use of lastcomp

Now that a copy of the rsp->completed flag is available in all rcu_node
structures, make full use of it.  It is still legitimate to access
rsp->completed while holding the root rcu_node structure's lock, however.
Also, tighten up force_quiescent_state()'s checks for end of current
grace period.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcutree.c |   13 ++++++-------
 1 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f93f0e2..1089d08 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -817,7 +817,7 @@ cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
 
 	rnp = rdp->mynode;
 	spin_lock_irqsave(&rnp->lock, flags);
-	if (lastcomp != ACCESS_ONCE(rsp->completed)) {
+	if (lastcomp != rnp->completed) {
 
 		/*
 		 * Someone beat us to it for this grace period, so leave.
@@ -935,7 +935,6 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
 static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
 {
 	unsigned long flags;
-	long lastcomp;
 	unsigned long mask;
 	struct rcu_data *rdp = rsp->rda[cpu];
 	struct rcu_node *rnp;
@@ -958,7 +957,6 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
 		spin_unlock(&rnp->lock);	/* irqs remain disabled. */
 		rnp = rnp->parent;
 	} while (rnp != NULL);
-	lastcomp = rsp->completed;
 
 	spin_unlock_irqrestore(&rsp->onofflock, flags);
 
@@ -1132,7 +1130,7 @@ static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
 	rcu_for_each_leaf_node(rsp, rnp) {
 		mask = 0;
 		spin_lock_irqsave(&rnp->lock, flags);
-		if (rsp->completed != lastcomp) {
+		if (rnp->completed != lastcomp) {
 			spin_unlock_irqrestore(&rnp->lock, flags);
 			return 1;
 		}
@@ -1146,7 +1144,7 @@ static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
 			if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
 				mask |= bit;
 		}
-		if (mask != 0 && rsp->completed == lastcomp) {
+		if (mask != 0 && rnp->completed == lastcomp) {
 
 			/* cpu_quiet_msk() releases rnp->lock. */
 			cpu_quiet_msk(mask, rsp, rnp, flags);
@@ -1183,7 +1181,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 	lastcomp = rsp->gpnum - 1;
 	signaled = rsp->signaled;
 	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
-	if (lastcomp == rsp->gpnum) {
+	if(!rcu_gp_in_progress(rsp)) {
 		rsp->n_force_qs_ngp++;
 		spin_unlock(&rnp->lock);
 		goto unlock_ret;  /* no GP in progress, time updated. */
@@ -1211,7 +1209,8 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 		/* Update state, record completion counter. */
 		forcenow = 0;
 		spin_lock(&rnp->lock);
-		if (lastcomp == rsp->completed &&
+		if (lastcomp + 1 == rsp->gpnum &&
+		    lastcomp == rsp->completed &&
 		    rsp->signaled == signaled) {
 			rsp->signaled = RCU_FORCE_QS;
 			rsp->completed_fqs = lastcomp;
-- 
1.5.2.5

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