[PATCH 08/10] rcu: Implement PCPU_RCU_PREEMPT_COUNT framework

[Lai Jiangshan <jiangshanlai@gmail.com>]

From: Lai Jiangshan <jiangshan.ljs@antgroup.com>

When the arch code provides HAVE_PCPU_RCU_PREEMPT_COUNT and the
corresponding functions, rcu_preempt core uses the functions to
implement rcu_read_[un]lock, rcu_preempt_depth(), special bits,
switching and so on.

Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
---
 include/linux/rcupdate.h | 33 +++++++++++++++++++++++++++++++++
 kernel/rcu/Kconfig       |  8 ++++++++
 kernel/rcu/rcu.h         |  4 ++++
 kernel/rcu/tree_plugin.h |  8 ++++++++
 4 files changed, 53 insertions(+)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index cc77d76a870b..bf369741ef93 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -70,6 +70,8 @@ static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned
 
 void rcu_read_unlock_special(void);
 
+#ifndef CONFIG_PCPU_RCU_PREEMPT_COUNT
+
 void __rcu_read_lock(void);
 void __rcu_read_unlock(void);
 
@@ -81,6 +83,37 @@ void __rcu_read_unlock(void);
  */
 #define rcu_preempt_depth() READ_ONCE(current->rcu_read_lock_nesting)
 #define rcu_preempt_depth_set(val) WRITE_ONCE(current->rcu_read_lock_nesting, (val))
+#define pcpu_rcu_preempt_special_set() do { } while (0)
+#define pcpu_rcu_preempt_special_clear() do { } while (0)
+
+#else /* #ifndef CONFIG_PCPU_RCU_PREEMPT_COUNT */
+
+#include <asm/rcu_preempt.h>
+
+static __always_inline void __rcu_read_lock(void)
+{
+	pcpu_rcu_preempt_count_add(1);
+	barrier();
+}
+
+static __always_inline void __rcu_read_unlock(void)
+{
+	barrier();
+	if (unlikely(pcpu_rcu_preempt_count_dec_and_test()))
+		pcpu_rcu_read_unlock_special();
+}
+
+static inline int rcu_preempt_depth(void)
+{
+	return pcpu_rcu_preempt_count();
+}
+
+static inline void rcu_preempt_depth_set(int val)
+{
+	pcpu_rcu_preempt_count_set(val);
+}
+
+#endif /* #else #ifndef CONFIG_PCPU_RCU_PREEMPT_COUNT */
 
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index e7d2dd267593..5d91147bc9a3 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -345,4 +345,12 @@ config RCU_DOUBLE_CHECK_CB_TIME
 	  Say Y here if you need tighter callback-limit enforcement.
 	  Say N here if you are unsure.
 
+config HAVE_PCPU_RCU_PREEMPT_COUNT
+	bool
+
+config PCPU_RCU_PREEMPT_COUNT
+	def_bool y
+	depends on PREEMPT_RCU && HAVE_PCPU_RCU_PREEMPT_COUNT
+	depends on !PROVE_LOCKING && !RCU_STRICT_GRACE_PERIOD
+
 endmenu # "RCU Subsystem"
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index ea5ae957c687..2322b040c5cd 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -671,6 +671,10 @@ static inline int rcu_stall_notifier_call_chain(unsigned long val, void *v) { re
 static inline void
 rcu_preempt_switch(struct task_struct *prev, struct task_struct *next)
 {
+#ifdef CONFIG_PCPU_RCU_PREEMPT_COUNT
+	prev->rcu_read_lock_nesting = rcu_preempt_depth();
+	pcpu_rcu_preempt_switch(next->rcu_read_lock_nesting, next->rcu_read_unlock_special.s);
+#endif // #ifdef CONFIG_PCPU_RCU_PREEMPT_COUNT
 }
 
 #endif /* __KERNEL_RCU_H */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 880b3fef1158..db68d0c1c1f2 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -107,10 +107,13 @@ static bool sync_rcu_exp_done(struct rcu_node *rnp);
 
 #define set_rcu_preempt_special(reason)	do {				\
 	WRITE_ONCE(current->rcu_read_unlock_special.b.reason, true);	\
+	pcpu_rcu_preempt_special_set();					\
 	} while (0)
 
 #define clear_rcu_preempt_special(reason)	do {			\
 	WRITE_ONCE(current->rcu_read_unlock_special.b.reason, false);	\
+	if (!current->rcu_read_unlock_special.s)			\
+		pcpu_rcu_preempt_special_clear();			\
 	} while (0)
 
 /*
@@ -379,6 +382,8 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
 	return READ_ONCE(rnp->gp_tasks) != NULL;
 }
 
+#ifndef CONFIG_PCPU_RCU_PREEMPT_COUNT
+
 /* limit value for ->rcu_read_lock_nesting. */
 #define RCU_NEST_PMAX (INT_MAX / 2)
 
@@ -436,6 +441,8 @@ void __rcu_read_unlock(void)
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 
+#endif /* #ifndef CONFIG_PCPU_RCU_PREEMPT_COUNT */
+
 /*
  * Advance a ->blkd_tasks-list pointer to the next entry, instead
  * returning NULL if at the end of the list.
@@ -489,6 +496,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 		return;
 	}
 	t->rcu_read_unlock_special.s = 0;
+	pcpu_rcu_preempt_special_clear();
 	if (special.b.need_qs) {
 		if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
 			rdp->cpu_no_qs.b.norm = false;
-- 
2.19.1.6.gb485710b