[patch V5 11/38] rcu: Provide __rcu_is_watching()

Thomas Gleixner
2020-05-12T22:23:26Z

Same as rcu_is_watching() but without the preempt_disable/enable() pair
inside the function. It is merked noinstr so it ends up in the
non-instrumentable text section.

This is useful for non-preemptible code especially in the low level entry
section. Using rcu_is_watching() there results in a call to the
preempt_schedule_notrace() thunk which triggers noinstr section warnings in
objtool.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V5: New patch
---
include/linux/rcutiny.h | 1 +
include/linux/rcutree.h | 1 +
kernel/rcu/tree.c | 5 +++++
3 files changed, 7 insertions(+)

--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -86,6 +86,7 @@ static inline void rcu_scheduler_startin
static inline void rcu_end_inkernel_boot(void) { }
static inline bool rcu_inkernel_boot_has_ended(void) { return true; }
static inline bool rcu_is_watching(void) { return true; }
+static inline bool __rcu_is_watching(void) { return true; }
static inline void rcu_momentary_dyntick_idle(void) { }
static inline void kfree_rcu_scheduler_running(void) { }
static inline bool rcu_gp_might_be_stalled(void) { return false; }
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -58,6 +58,7 @@ extern int rcu_scheduler_active __read_m
void rcu_end_inkernel_boot(void);
bool rcu_inkernel_boot_has_ended(void);
bool rcu_is_watching(void);
+bool __rcu_is_watching(void);
#ifndef CONFIG_PREEMPTION
void rcu_all_qs(void);
#endif
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -984,6 +984,11 @@ static void rcu_disable_urgency_upon_qs(
}
}

+noinstr bool __rcu_is_watching(void)
+{
+ return !rcu_dynticks_curr_cpu_in_eqs();
+}
+
/**
* rcu_is_watching - see if RCU thinks that the current CPU is not idle
*