linux-kernel - [patch V5 11/38] rcu: Provide __rcu_is

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Date:   Tue, 12 May 2020 23:01:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [patch V5 11/38] rcu: Provide __rcu_is_watching()

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@...utronix.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
  *