linux-kernel - [tip:core/rcu] rcu: Eliminate rcu_process

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Date:	Wed, 13 Jan 2010 10:26:25 GMT
From:	"tip-bot for Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:core/rcu] rcu: Eliminate rcu_process_dyntick() return value

Commit-ID:  0f10dc826646134dce3e5751512b87d30f3903e4
Gitweb:     http://git.kernel.org/tip/0f10dc826646134dce3e5751512b87d30f3903e4
Author:     Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
AuthorDate: Mon, 4 Jan 2010 15:09:06 -0800
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 13 Jan 2010 09:06:03 +0100

rcu: Eliminate rcu_process_dyntick() return value

Because a new grace period cannot start while we are executing
within the force_quiescent_state() function's switch statement,
if any test within that switch statement or within any function
called from that switch statement shows that the current grace
period has ended, we can safely re-do that test any time before
we leave the switch statement.  This means that we no longer
need a return value from rcu_process_dyntick(), as we can simply
invoke rcu_gp_in_progress() to check whether the old grace
period has finished -- there is no longer any need to worry
about whether or not a new grace period has been started.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: laijs@...fujitsu.com
Cc: dipankar@...ibm.com
Cc: mathieu.desnoyers@...ymtl.ca
Cc: josh@...htriplett.org
Cc: dvhltc@...ibm.com
Cc: niv@...ibm.com
Cc: peterz@...radead.org
Cc: rostedt@...dmis.org
Cc: Valdis.Kletnieks@...edu
Cc: dhowells@...hat.com
LKML-Reference: <12626465501857-git-send-email->
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/rcutree.c |   17 ++++++-----------
 1 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c7d0070..e497119 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1144,11 +1144,9 @@ void rcu_check_callbacks(int cpu, int user)
 /*
  * Scan the leaf rcu_node structures, processing dyntick state for any that
  * have not yet encountered a quiescent state, using the function specified.
- * Returns 1 if the current grace period ends while scanning (possibly
- * because we made it end).
  */
-static int rcu_process_dyntick(struct rcu_state *rsp,
-			       int (*f)(struct rcu_data *))
+static void rcu_process_dyntick(struct rcu_state *rsp,
+				int (*f)(struct rcu_data *))
 {
 	unsigned long bit;
 	int cpu;
@@ -1161,7 +1159,7 @@ static int rcu_process_dyntick(struct rcu_state *rsp,
 		spin_lock_irqsave(&rnp->lock, flags);
 		if (rnp->completed != rsp->gpnum - 1) {
 			spin_unlock_irqrestore(&rnp->lock, flags);
-			return 1;
+			return;
 		}
 		if (rnp->qsmask == 0) {
 			spin_unlock_irqrestore(&rnp->lock, flags);
@@ -1181,7 +1179,6 @@ static int rcu_process_dyntick(struct rcu_state *rsp,
 		}
 		spin_unlock_irqrestore(&rnp->lock, flags);
 	}
-	return 0;
 }
 
 /*
@@ -1193,7 +1190,6 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 	unsigned long flags;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 	u8 forcenow;
-	u8 gpdone;
 
 	if (!rcu_gp_in_progress(rsp))
 		return;  /* No grace period in progress, nothing to force. */
@@ -1226,10 +1222,9 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 			break; /* So gcc recognizes the dead code. */
 
 		/* Record dyntick-idle state. */
-		gpdone = rcu_process_dyntick(rsp,
-					     dyntick_save_progress_counter);
+		rcu_process_dyntick(rsp, dyntick_save_progress_counter);
 		spin_lock(&rnp->lock);  /* irqs already disabled */
-		if (gpdone)
+		if (!rcu_gp_in_progress(rsp))
 			break;
 		/* fall into next case. */
 
@@ -1249,7 +1244,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 
 		/* Check dyntick-idle state, send IPI to laggarts. */
 		spin_unlock(&rnp->lock);  /* irqs remain disabled */
-		gpdone = rcu_process_dyntick(rsp, rcu_implicit_dynticks_qs);
+		rcu_process_dyntick(rsp, rcu_implicit_dynticks_qs);
 
 		/* Leave state in case more forcing is required. */
 
--
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