[3.16.y-ckt stable] Patch "PM / sleep / x86: Fix crash on graph trace through x86 suspend" has been added to the 3.16.y-ckt tree

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    PM / sleep / x86: Fix crash on graph trace through x86 suspend

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt26.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

---8<------------------------------------------------------------

>From 2ea803d5b0f352b9c7ce232dcdc3eb6384068220 Mon Sep 17 00:00:00 2001
From: Todd E Brandt <todd.e.brandt at linux.intel.com>
Date: Wed, 2 Mar 2016 16:05:29 -0800
Subject: PM / sleep / x86: Fix crash on graph trace through x86 suspend

commit 92f9e179a702a6adbc11e2fedc76ecd6ffc9e3f7 upstream.

Pause/unpause graph tracing around do_suspend_lowlevel as it has
inconsistent call/return info after it jumps to the wakeup vector.
The graph trace buffer will otherwise become misaligned and
may eventually crash and hang on suspend.

To reproduce the issue and test the fix:
Run a function_graph trace over suspend/resume and set the graph
function to suspend_devices_and_enter. This consistently hangs the
system without this fix.

Signed-off-by: Todd Brandt <todd.e.brandt at linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/kernel/acpi/sleep.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 31368207837c..8255d2fe8cfa 100644
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -16,6 +16,7 @@
 #include <asm/cacheflush.h>
 #include <asm/realmode.h>

+#include <linux/ftrace.h>
 #include "../../realmode/rm/wakeup.h"
 #include "sleep.h"

@@ -107,7 +108,13 @@ int x86_acpi_suspend_lowlevel(void)
        saved_magic = 0x123456789abcdef0L;
 #endif /* CONFIG_64BIT */

+	/*
+	 * Pause/unpause graph tracing around do_suspend_lowlevel as it has
+	 * inconsistent call/return info after it jumps to the wakeup vector.
+	 */
+	pause_graph_tracing();
 	do_suspend_lowlevel();
+	unpause_graph_tracing();
 	return 0;
 }