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>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index eae331d..d42ad30 100644 (file)
--- 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);
 }