From a43bff3a27b8cec777ea90465547c59c89349d8b Mon Sep 17 00:00:00 2001
From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Date: Thu, 19 Apr 2018 12:34:03 +0530
Subject: [PATCH 4/9] powerpc64/ftrace: Delay enabling ftrace on secondary cpus

References: bsc#1088804
Patch-mainline: v4.18-rc1
Git-commit: d103978636c27fce216bbc8bb289981047b71bd4

On the boot cpu, though we enable paca->ftrace_enabled in early_setup()
(via cpu_ready_for_interrupts()), we don't start tracing until much
later since ftrace is not initialized yet and since we only support
DYNAMIC_FTRACE on powerpc. However, it is possible that ftrace has been
initialized by the time some of the secondary cpus start up. In this
case, we will try to trace some of the early boot code which can cause
problems.

To address this, move setting paca->ftrace_enabled from
cpu_ready_for_interrupts() to early_setup() for the boot cpu, and towards
the end of start_secondary() for secondary cpus.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
 arch/powerpc/kernel/setup_64.c | 10 +++++++---
 arch/powerpc/kernel/smp.c      |  4 ++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 741bd0a3534c..25e11b6f429a 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -249,9 +249,6 @@ static void cpu_ready_for_interrupts(void)
 
 	/* Set IR and DR in PACA MSR */
 	get_paca()->kernel_msr = MSR_KERNEL;
-
-	/* We are now ok to enable ftrace */
-	get_paca()->ftrace_enabled = 1;
 }
 
 /*
@@ -327,6 +324,13 @@ void __init early_setup(unsigned long dt_ptr)
 	 */
 	cpu_ready_for_interrupts();
 
+	/*
+	 * We enable ftrace here, but since we only support DYNAMIC_FTRACE, it
+	 * will only actually get enabled on the boot cpu much later once
+	 * ftrace itself has been initialized.
+	 */
+	this_cpu_enable_ftrace();
+
 	DBG(" <- early_setup()\n");
 
 #ifdef CONFIG_PPC_EARLY_DEBUG_BOOTX
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index ec186e767d1c..0d50ca3aa876 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -59,6 +59,7 @@
 #include <asm/kexec.h>
 #include <asm/asm-prototypes.h>
 #include <asm/cpu_has_feature.h>
+#include <asm/ftrace.h>
 
 #ifdef DEBUG
 #include <asm/udbg.h>
@@ -952,6 +953,9 @@ void start_secondary(void *unused)
 
 	local_irq_enable();
 
+	/* We can enable ftrace for secondary cpus now */
+	this_cpu_enable_ftrace();
+
 	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
 
 	BUG();
-- 
2.13.6