rcu: Abstract the dynticks snapshot operation
This commit is the second step towards full abstraction of all accesses to
the ->dynticks counter, implementing the previously open-coded atomic
add of zero in a new rcu_dynticks_snap() function. This abstraction will
ease changes o the ->dynticks counter operation.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 14e283c..805d55e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -282,6 +282,17 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
};
/*
+ * Snapshot the ->dynticks counter with full ordering so as to allow
+ * stable comparison of this counter with past and future snapshots.
+ */
+static int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
+{
+ int snap = atomic_add_return(0, &rdtp->dynticks);
+
+ return snap;
+}
+
+/*
* Do a double-increment of the ->dynticks counter to emulate a
* momentary idle-CPU quiescent state.
*/
@@ -1049,7 +1060,9 @@ void rcu_nmi_exit(void)
*/
bool notrace __rcu_is_watching(void)
{
- return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
+ struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
+
+ return atomic_read(&rdtp->dynticks) & 0x1;
}
/**
@@ -1132,7 +1145,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
static int dyntick_save_progress_counter(struct rcu_data *rdp,
bool *isidle, unsigned long *maxj)
{
- rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
+ rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
rcu_sysidle_check_cpu(rdp, isidle, maxj);
if ((rdp->dynticks_snap & 0x1) == 0) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
@@ -1157,7 +1170,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
int *rcrmp;
unsigned int snap;
- curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
+ curr = (unsigned int)rcu_dynticks_snap(rdp->dynticks);
snap = (unsigned int)rdp->dynticks_snap;
/*