rcu: Remove leg of force_quiescent_state() switch statement

The comparisons of rsp->gpnum nad rsp->completed in
rcu_process_dyntick() and force_quiescent_state() can be
replaced by the much more clear rcu_gp_in_progress() predicate
function.  After doing this, it becomes clear that the
RCU_SAVE_COMPLETED leg of the force_quiescent_state() function's
switch statement is almost completely a no-op.  A small change
to the RCU_SAVE_DYNTICK leg renders it a complete no-op, after
which it can be removed.  Doing so also eliminates the forcenow
local variable from force_quiescent_state().

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: <12626465501781-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 17 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index e4971192fa9c..6268f37adfc4 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1144,6 +1144,7 @@ void rcu_check_callbacks(int cpu, int user)
 /*
  * Scan the leaf rcu_node structures, processing dyntick state for any that
  * have not yet encountered a quiescent state, using the function specified.
+ * The caller must have suppressed start of new grace periods.
  */
 static void rcu_process_dyntick(struct rcu_state *rsp,
                                 int (*f)(struct rcu_data *))
@@ -1157,7 +1158,7 @@ static void rcu_process_dyntick(struct rcu_state *rsp,
         rcu_for_each_leaf_node(rsp, rnp) {
                 mask = 0;
                 spin_lock_irqsave(&rnp->lock, flags);
-                if (rnp->completed != rsp->gpnum - 1) {
+                if (!rcu_gp_in_progress(rsp)) {
                         spin_unlock_irqrestore(&rnp->lock, flags);
                         return;
                 }
@@ -1171,7 +1172,7 @@ static void rcu_process_dyntick(struct rcu_state *rsp,
                         if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
                                 mask |= bit;
                 }
-                if (mask != 0 && rnp->completed == rsp->gpnum - 1) {
+                if (mask != 0 && rcu_gp_in_progress(rsp)) {
 
                         /* rcu_report_qs_rnp() releases rnp->lock. */
                         rcu_report_qs_rnp(mask, rsp, rnp, flags);
@@ -1189,7 +1190,6 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 {
         unsigned long flags;
         struct rcu_node *rnp = rcu_get_root(rsp);
-        u8 forcenow;
 
         if (!rcu_gp_in_progress(rsp))
                 return;  /* No grace period in progress, nothing to force. */
@@ -1224,21 +1224,9 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
                 /* Record dyntick-idle state. */
                 rcu_process_dyntick(rsp, dyntick_save_progress_counter);
                 spin_lock(&rnp->lock);  /* irqs already disabled */
-                if (!rcu_gp_in_progress(rsp))
-                        break;
-                /* fall into next case. */
-
-        case RCU_SAVE_COMPLETED:
-
-                /* Update state, record completion counter. */
-                forcenow = 0;
-                if (rsp->gpnum - 1 == rsp->completed) {
-                        forcenow = rsp->signaled == RCU_SAVE_COMPLETED;
+                if (rcu_gp_in_progress(rsp))
                         rsp->signaled = RCU_FORCE_QS;
-                }
-                if (!forcenow)
-                        break;
-                /* fall into next case. */
+                break;
 
         case RCU_FORCE_QS: