rcu: Eliminate rcu_process_dyntick() return value

Because a new grace period cannot start while we are executing
within the force_quiescent_state() function's switch statement,
if any test within that switch statement or within any function
called from that switch statement shows that the current grace
period has ended, we can safely re-do that test any time before
we leave the switch statement.  This means that we no longer
need a return value from rcu_process_dyntick(), as we can simply
invoke rcu_gp_in_progress() to check whether the old grace
period has finished -- there is no longer any need to worry
about whether or not a new grace period has been started.

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: <12626465501857-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c7d0070..e497119 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1144,11 +1144,9 @@ 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.
- * Returns 1 if the current grace period ends while scanning (possibly
- * because we made it end).
  */
-static int rcu_process_dyntick(struct rcu_state *rsp,
-                              int (*f)(struct rcu_data *))
+static void rcu_process_dyntick(struct rcu_state *rsp,
+                               int (*f)(struct rcu_data *))
 {
        unsigned long bit;
        int cpu;
@@ -1161,7 +1159,7 @@ static int rcu_process_dyntick(struct rcu_state *rsp,
                spin_lock_irqsave(&rnp->lock, flags);
                if (rnp->completed != rsp->gpnum - 1) {
                        spin_unlock_irqrestore(&rnp->lock, flags);
-                       return 1;
+                       return;
                }
                if (rnp->qsmask == 0) {
                        spin_unlock_irqrestore(&rnp->lock, flags);
@@ -1181,7 +1179,6 @@ static int rcu_process_dyntick(struct rcu_state *rsp,
                }
                spin_unlock_irqrestore(&rnp->lock, flags);
        }
-       return 0;
 }
 
 /*
@@ -1193,7 +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;
-       u8 gpdone;
 
        if (!rcu_gp_in_progress(rsp))
                return;  /* No grace period in progress, nothing to force. */
@@ -1226,10 +1222,9 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
                        break; /* So gcc recognizes the dead code. */
 
                /* Record dyntick-idle state. */
-               gpdone = rcu_process_dyntick(rsp,
-                                            dyntick_save_progress_counter);
+               rcu_process_dyntick(rsp, dyntick_save_progress_counter);
                spin_lock(&rnp->lock);  /* irqs already disabled */
-               if (gpdone)
+               if (!rcu_gp_in_progress(rsp))
                        break;
                /* fall into next case. */
 
@@ -1249,7 +1244,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 
                /* Check dyntick-idle state, send IPI to laggarts. */
                spin_unlock(&rnp->lock);  /* irqs remain disabled */
-               gpdone = rcu_process_dyntick(rsp, rcu_implicit_dynticks_qs);
+               rcu_process_dyntick(rsp, rcu_implicit_dynticks_qs);
 
                /* Leave state in case more forcing is required. */