[PATCH 1/3 RFC paul/rcu/srcu] srcu: Remove fast check path

[Lai Jiangshan]

This fast check path is used for optimizing the situation
that there are many concurrently update site.

But we have no suck situation in currect kernel.
And it introduces complexity, so we just remove it.

Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
---
 kernel/srcu.c |   25 +------------------------
 1 files changed, 1 insertions(+), 24 deletions(-)

diff --git a/kernel/srcu.c b/kernel/srcu.c
index 84c9b97..17e95bc 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -308,7 +308,7 @@ static void flip_idx_and_wait(struct srcu_struct *sp, bool expedited)
  */
 static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
 {
-	int idx;
+	int idx = 0;
 
 	rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
 			   !lock_is_held(&rcu_bh_lock_map) &&
@@ -316,32 +316,9 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
 			   !lock_is_held(&rcu_sched_lock_map),
 			   "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
 
-	smp_mb();  /* Ensure prior action happens before grace period. */
-	idx = ACCESS_ONCE(sp->completed);
-	smp_mb();  /* Access to ->completed before lock acquisition. */
 	mutex_lock(&sp->mutex);
 
 	/*
-	 * Check to see if someone else did the work for us while we were
-	 * waiting to acquire the lock.  We need -three- advances of
-	 * the counter, not just one.  If there was but one, we might have
-	 * shown up -after- our helper's first synchronize_sched(), thus
-	 * having failed to prevent CPU-reordering races with concurrent
-	 * srcu_read_unlock()s on other CPUs (see comment below).  If there
-	 * was only two, we are guaranteed to have waited through only one
-	 * full index-flip phase.  So we either (1) wait for three or
-	 * (2) supply the additional ones we need.
-	 */
-
-	if (sp->completed == idx + 2)
-		idx = 1;
-	else if (sp->completed == idx + 3) {
-		mutex_unlock(&sp->mutex);
-		return;
-	} else
-		idx = 0;
-
-	/*
 	 * If there were no helpers, then we need to do two flips of
 	 * the index.  The first flip is required if there are any
 	 * outstanding SRCU readers even if there are no new readers
-- 
1.7.4.4
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