[RFC/WIP PATCH 3/4] rcuscale: add hazptr scale type

[Kunwu Chan <kunwu.chan@gmail.com>]

Add hazptr reader and synchronize operations so that synchronize
latency can be measured alongside RCU and SRCU.

The read side acquires the hazard pointer in readlock() and holds
it until readunlock(), matching the RCU/SRCU reader model.  The
address of a static object serves as the synchronize target, which
is stable and never reclaimed.  Both normal and expedited sync map
to hazptr_synchronize(), since hazptr has no expedited concept.

Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 kernel/rcu/rcuscale.c | 65 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 64 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 1097ec15879c..072ddf9526c3 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -39,6 +39,7 @@
 #include <linux/torture.h>
 #include <linux/vmalloc.h>
 #include <linux/rcupdate_trace.h>
+#include <linux/hazptr.h>
 #include <linux/sched/debug.h>
 
 #include "rcu.h"
@@ -418,6 +419,66 @@ static struct rcu_scale_ops tasks_tracing_ops = {
 
 #endif // #else // #ifdef CONFIG_TASKS_TRACE_RCU
 
+#if IS_ENABLED(CONFIG_HAZPTR_TORTURE_TEST)
+
+static int hazptr_scale_obj;	/* Stable, non-NULL, never reclaimed. */
+static void *hazptr_scale_ptr = &hazptr_scale_obj;
+
+struct hazptr_scale_state {
+	struct hazptr_ctx ctx;
+	void *addr;
+};
+static DEFINE_PER_CPU(struct hazptr_scale_state, hazptr_scale_state);
+
+static int hazptr_scale_read_lock(void)
+{
+	struct hazptr_scale_state *state = this_cpu_ptr(&hazptr_scale_state);
+
+	preempt_disable();
+	state->addr = hazptr_acquire(&state->ctx, &hazptr_scale_ptr);
+	return 0;
+}
+
+static void hazptr_scale_read_unlock(int idx)
+{
+	struct hazptr_scale_state *state = this_cpu_ptr(&hazptr_scale_state);
+
+	udelay(10);
+	hazptr_release(&state->ctx, state->addr);
+	preempt_enable();
+}
+
+static unsigned long hazptr_scale_completed(void)
+{
+	return 0;
+}
+
+static void hazptr_scale_sync(void)
+{
+	hazptr_synchronize(hazptr_scale_ptr);
+}
+
+static void hazptr_scale_sync_exp(void)
+{
+	hazptr_synchronize(hazptr_scale_ptr);
+}
+
+static struct rcu_scale_ops hazptr_scale_ops = {
+	.ptype		= 0,
+	.readlock	= hazptr_scale_read_lock,
+	.readunlock	= hazptr_scale_read_unlock,
+	.get_gp_seq	= hazptr_scale_completed,
+	.gp_diff	= NULL,
+	.sync		= hazptr_scale_sync,
+	.exp_sync	= hazptr_scale_sync_exp,
+	.name		= "hazptr",
+};
+
+#define HAZPTR_SCALE_OPS &hazptr_scale_ops,
+#else
+#define HAZPTR_SCALE_OPS
+#endif
+
 static unsigned long rcuscale_seq_diff(unsigned long new, unsigned long old)
 {
 	if (!cur_ops->gp_diff)
@@ -1110,7 +1171,9 @@ rcu_scale_init(void)
 	long i;
 	long j;
 	static struct rcu_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &srcud_ops, TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
+		&rcu_ops, &srcu_ops, &srcud_ops,
+		TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
+		HAZPTR_SCALE_OPS
 	};
 
 	if (!torture_init_begin(scale_type, verbose))
-- 
2.43.0