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>

1 files changed, 3 insertions, 10 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index eae331da6be..d42ad30c4d7 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);
 }