linux-kernel - [PATCH 4/6] remove flip_idx_and

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Date:	Tue, 6 Mar 2012 17:57:36 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: [PATCH 4/6] remove flip_idx_and_wait()

flip and check are the basic steps of gp. call them directly.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
 kernel/srcu.c |   35 +++++++++++++++++------------------
 1 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/kernel/srcu.c b/kernel/srcu.c
index d5f3450..d101ed5 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -300,23 +300,12 @@ static void wait_idx(struct srcu_struct *sp, int idx, int trycount)
 }
 
 /*
- * Flip the readers' index by incrementing ->completed, then wait
- * until there are no more readers using the counters referenced by
- * the old index value.  (Recall that the index is the bottom bit
- * of ->completed.)
- *
- * Of course, it is possible that a reader might be delayed for the
- * full duration of flip_idx_and_wait() between fetching the
- * index and incrementing its counter.  This possibility is handled
- * by the next __synchronize_srcu() invoking wait_idx() for such readers
- * before starting a new grace period.
+ * Flip the readers' index by incrementing ->completed, then new
+ * readers will use counters referenced on new index value.
  */
-static void flip_idx_and_wait(struct srcu_struct *sp, int trycount)
+static void srcu_flip(struct srcu_struct *sp)
 {
-	int idx;
-
-	idx = sp->completed++ & 0x1;
-	wait_idx(sp, idx, trycount);
+	ACCESS_ONCE(sp->completed)++;
 }
 
 /*
@@ -362,10 +351,20 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 
 	/*
 	 * Now that wait_idx() has waited for the really old readers,
-	 * invoke flip_idx_and_wait() to flip the counter and wait
-	 * for current SRCU readers.
+	 *
+	 * Flip the readers' index by incrementing ->completed, then wait
+	 * until there are no more readers using the counters referenced by
+	 * the old index value.  (Recall that the index is the bottom bit
+	 * of ->completed.)
+	 *
+	 * Of course, it is possible that a reader might be delayed for the
+	 * full duration of flip_idx_and_wait() between fetching the
+	 * index and incrementing its counter.  This possibility is handled
+	 * by the next __synchronize_srcu() invoking wait_idx() for such
+	 * readers before starting a new grace period.
 	 */
-	flip_idx_and_wait(sp, trycount);
+	srcu_flip(sp);
+	wait_idx(sp, (sp->completed - 1) & 0x1, trycount);
 
 	mutex_unlock(&sp->mutex);
 }
-- 
1.7.4.4

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