linux-kernel - [PATCH 5/8] x86,tracing: Mark debug_stack_{set

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Date:   Wed, 12 Feb 2020 10:32:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        rostedt@...dmis.org
Cc:     peterz@...radead.org, mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com
Subject: [PATCH 5/8] x86,tracing: Mark debug_stack_{set_zero,reset)() notrace

Because do_nmi() must not call into tracing outside of
nmi_enter()/nmi_exit(), these functions must be notrace.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/cpu/common.c |    4 ++--
 arch/x86/kernel/nmi.c        |    6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1690,14 +1690,14 @@ void syscall_init(void)
 DEFINE_PER_CPU(int, debug_stack_usage);
 DEFINE_PER_CPU(u32, debug_idt_ctr);
 
-void debug_stack_set_zero(void)
+void notrace debug_stack_set_zero(void)
 {
 	this_cpu_inc(debug_idt_ctr);
 	load_current_idt();
 }
 NOKPROBE_SYMBOL(debug_stack_set_zero);
 
-void debug_stack_reset(void)
+void notrace debug_stack_reset(void)
 {
 	if (WARN_ON(!this_cpu_read(debug_idt_ctr)))
 		return;
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -534,6 +534,9 @@ do_nmi(struct pt_regs *regs, long error_
 	}
 #endif
 
+	/*
+	 * It is important that no tracing happens before nmi_enter()!
+	 */
 	nmi_enter();
 
 	inc_irq_stat(__nmi_count);
@@ -542,6 +545,9 @@ do_nmi(struct pt_regs *regs, long error_
 		default_do_nmi(regs);
 
 	nmi_exit();
+	/*
+	 * No tracing after nmi_exit()!
+	 */
 
 #ifdef CONFIG_X86_64
 	if (unlikely(this_cpu_read(update_debug_stack))) {