linux-kernel - [PATCH 1/6] x86/entry: Clarify irq_{enter,exit}

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Message-ID: <20200527155003.131379869@infradead.org>
Date:   Wed, 27 May 2020 17:45:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, will@...nel.org, tglx@...utronix.de
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        a.darwish@...utronix.de, rostedt@...dmis.org,
        bigeasy@...utronix.de, peterz@...radead.org
Subject: [PATCH 1/6] x86/entry: Clarify irq_{enter,exit}_rcu()

Because:

  irq_enter_rcu() includes lockdep_hardirq_enter()
  irq_exit_rcu() does *NOT* include lockdep_hardirq_exit()

Which resulted two 'stray' lockdep_hardirq_exit() calls in idtentry.h,
and me spending a long time trying to find the matching enters.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/idtentry.h |    2 --
 kernel/softirq.c                |   19 +++++++++++++------
 2 files changed, 13 insertions(+), 8 deletions(-)

--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -206,7 +206,6 @@ __visible noinstr void func(struct pt_re
 	kvm_set_cpu_l1tf_flush_l1d();					\
 	__##func (regs, (u8)error_code);				\
 	irq_exit_rcu();							\
-	lockdep_hardirq_exit();						\
 	instrumentation_end();						\
 	idtentry_exit_cond_rcu(regs, rcu_exit);				\
 }									\
@@ -249,7 +248,6 @@ __visible noinstr void func(struct pt_re
 	kvm_set_cpu_l1tf_flush_l1d();					\
 	run_on_irqstack_cond(__##func, regs, regs);			\
 	irq_exit_rcu();							\
-	lockdep_hardirq_exit();						\
 	instrumentation_end();						\
 	idtentry_exit_cond_rcu(regs, rcu_exit);				\
 }									\
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -404,12 +404,7 @@ static inline void tick_irq_exit(void)
 #endif
 }
 
-/**
- * irq_exit_rcu() - Exit an interrupt context without updating RCU
- *
- * Also processes softirqs if needed and possible.
- */
-void irq_exit_rcu(void)
+static inline void __irq_exit_rcu(void)
 {
 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
 	local_irq_disable();
@@ -425,6 +420,18 @@ void irq_exit_rcu(void)
 }
 
 /**
+ * irq_exit_rcu() - Exit an interrupt context without updating RCU
+ *
+ * Also processes softirqs if needed and possible.
+ */
+void irq_exit_rcu(void)
+{
+	__irq_exit_rcu();
+	 /* must be last! */
+	lockdep_hardirq_exit();
+}
+
+/**
  * irq_exit - Exit an interrupt context, update RCU and lockdep
  *
  * Also processes softirqs if needed and possible.