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Subject[PATCH RFC tip/core/rcu 07/18] rcu: eliminate rcu_process_dyntick() return value
Date
From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Proposed for 2.6.34, not for inclusion.

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>
---
kernel/rcutree.c | 17 ++++++-----------
1 files changed, 6 insertions(+), 11 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c7d0070..e497119 100644
--- 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. */

--
1.5.2.5


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