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

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