Mailing List Archive

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