Commit-ID: 281d150c5f8892f158747594ab49ce2823fd8b8c
Gitweb: http://git.kernel.org/tip/281d150c5f8892f158747594ab49ce2823fd8b8c
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Mon, 2 Nov 2009 13:52:27 -0800
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 10 Nov 2009 04:11:17 +0100
rcu: Prepare for synchronization fixes: clean up for non-NO_HZ handling of ->completed counter
Impose a clear locking design on non-NO_HZ handling of the
->completed counter. This increases the distance between the
RCU and the CPU-hotplug mechanisms.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: laijs@xxxxxxxxxxxxxx
Cc: dipankar@xxxxxxxxxx
Cc: mathieu.desnoyers@xxxxxxxxxx
Cc: josh@xxxxxxxxxxxxxxxx
Cc: dvhltc@xxxxxxxxxx
Cc: niv@xxxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: Valdis.Kletnieks@xxxxxx
Cc: dhowells@xxxxxxxxxx
Cc: <stable@xxxxxxxxxx> # .32.x
LKML-Reference: <12571987491353-git-send-email->
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
kernel/rcutree.c | 67 ++++++++++++++++++++++++-----------------------------
kernel/rcutree.h | 8 +++---
2 files changed, 34 insertions(+), 41 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 69f4efe..26249ab 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -178,9 +178,29 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
return &rsp->node[0];
}
+/*
+ * Record the specified "completed" value, which is later used to validate
+ * dynticks counter manipulations and CPU-offline checks. Specify
+ * "rsp->completed - 1" to unconditionally invalidate any future dynticks
+ * manipulations and CPU-offline checks. Such invalidation is useful at
+ * the beginning of a grace period.
+ */
+static void dyntick_record_completed(struct rcu_state *rsp, long comp)
+{
+ rsp->dynticks_completed = comp;
+}
+
#ifdef CONFIG_SMP
/*
+ * Recall the previously recorded value of the completion for dynticks.
+ */
+static long dyntick_recall_completed(struct rcu_state *rsp)
+{
+ return rsp->dynticks_completed;
+}
+
+/*
* If the specified CPU is offline, tell the caller that it is in
* a quiescent state. Otherwise, whack it with a reschedule IPI.
* Grace periods can end up waiting on an offline CPU when that
@@ -337,28 +357,9 @@ void rcu_irq_exit(void)
set_need_resched();
}
-/*
- * Record the specified "completed" value, which is later used to validate
- * dynticks counter manipulations. Specify "rsp->completed - 1" to
- * unconditionally invalidate any future dynticks manipulations (which is
- * useful at the beginning of a grace period).
- */
-static void dyntick_record_completed(struct rcu_state *rsp, long comp)
-{
- rsp->dynticks_completed = comp;
-}
-
#ifdef CONFIG_SMP
/*
- * Recall the previously recorded value of the completion for dynticks.
- */
-static long dyntick_recall_completed(struct rcu_state *rsp)
-{
- return rsp->dynticks_completed;
-}
-
-/*
* Snapshot the specified CPU's dynticks counter so that we can later
* credit them with an implicit quiescent state. Return 1 if this CPU
* is in dynticks idle mode, which is an extended quiescent state.
@@ -421,24 +422,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
#else /* #ifdef CONFIG_NO_HZ */
-static void dyntick_record_completed(struct rcu_state *rsp, long comp)
-{
-}
-
#ifdef CONFIG_SMP
-/*
- * If there are no dynticks, then the only way that a CPU can passively
- * be in a quiescent state is to be offline. Unlike dynticks idle, which
- * is a point in time during the prior (already finished) grace period,
- * an offline CPU is always in a quiescent state, and thus can be
- * unconditionally applied. So just return the current value of completed.
- */
-static long dyntick_recall_completed(struct rcu_state *rsp)
-{
- return rsp->completed;
-}
-
static int dyntick_save_progress_counter(struct rcu_data *rdp)
{
return 0;
@@ -1146,6 +1131,7 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
long lastcomp;
struct rcu_node *rnp = rcu_get_root(rsp);
u8 signaled;
+ u8 forcenow;
if (!rcu_gp_in_progress(rsp))
return; /* No grace period in progress, nothing to force. */
@@ -1182,16 +1168,23 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
if (rcu_process_dyntick(rsp, lastcomp,
dyntick_save_progress_counter))
goto unlock_ret;
+ /* fall into next case. */
+
+ case RCU_SAVE_COMPLETED:
/* Update state, record completion counter. */
+ forcenow = 0;
spin_lock(&rnp->lock);
if (lastcomp == rsp->completed &&
- rsp->signaled == RCU_SAVE_DYNTICK) {
+ rsp->signaled == signaled) {
rsp->signaled = RCU_FORCE_QS;
dyntick_record_completed(rsp, lastcomp);
+ forcenow = signaled == RCU_SAVE_COMPLETED;
}
spin_unlock(&rnp->lock);
- break;
+ if (!forcenow)
+ break;
+ /* fall into next case. */
case RCU_FORCE_QS:
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 1899023..8a4c165 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -204,11 +204,12 @@ struct rcu_data {
#define RCU_GP_IDLE 0 /* No grace period in progress. */
#define RCU_GP_INIT 1 /* Grace period being initialized. */
#define RCU_SAVE_DYNTICK 2 /* Need to scan dyntick state. */
-#define RCU_FORCE_QS 3 /* Need to force quiescent state. */
+#define RCU_SAVE_COMPLETED 3 /* Need to save rsp->completed. */
+#define RCU_FORCE_QS 4 /* Need to force quiescent state. */
#ifdef CONFIG_NO_HZ
#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
#else /* #ifdef CONFIG_NO_HZ */
-#define RCU_SIGNAL_INIT RCU_FORCE_QS
+#define RCU_SIGNAL_INIT RCU_SAVE_COMPLETED
#endif /* #else #ifdef CONFIG_NO_HZ */
#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */
@@ -274,9 +275,8 @@ struct rcu_state {
unsigned long jiffies_stall; /* Time at which to check */
/* for CPU stalls. */
#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
-#ifdef CONFIG_NO_HZ
long dynticks_completed; /* Value of completed @ snap. */
-#endif /* #ifdef CONFIG_NO_HZ */
+ /* Protected by fqslock. */
};
#ifdef RCU_TREE_NONCORE
--
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