Patch "arm64: kernel: pause/unpause function graph tracer in cpu_suspend()" has been added to the 4.1-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    arm64: kernel: pause/unpause function graph tracer in cpu_suspend()

to the 4.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm64-kernel-pause-unpause-function-graph-tracer-in-cpu_suspend.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From de818bd4522c40ea02a81b387d2fa86f989c9623 Mon Sep 17 00:00:00 2001
From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Date: Tue, 17 Nov 2015 11:50:51 +0000
Subject: arm64: kernel: pause/unpause function graph tracer in cpu_suspend()

From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

commit de818bd4522c40ea02a81b387d2fa86f989c9623 upstream.

The function graph tracer adds instrumentation that is required to trace
both entry and exit of a function. In particular the function graph
tracer updates the "return address" of a function in order to insert
a trace callback on function exit.

Kernel power management functions like cpu_suspend() are called
upon power down entry with functions called "finishers" that are in turn
called to trigger the power down sequence but they may not return to the
kernel through the normal return path.

When the core resumes from low-power it returns to the cpu_suspend()
function through the cpu_resume path, which leaves the trace stack frame
set-up by the function tracer in an incosistent state upon return to the
kernel when tracing is enabled.

This patch fixes the issue by pausing/resuming the function graph
tracer on the thread executing cpu_suspend() (ie the function call that
subsequently triggers the "suspend finishers"), so that the function graph
tracer state is kept consistent across functions that enter power down
states and never return by effectively disabling graph tracer while they
are executing.

Fixes: 819e50e25d0c ("arm64: Add ftrace support")
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arm64/kernel/suspend.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/arch/arm64/kernel/suspend.c
+++ b/arch/arm64/kernel/suspend.c
@@ -1,3 +1,4 @@
+#include <linux/ftrace.h>
 #include <linux/percpu.h>
 #include <linux/slab.h>
 #include <asm/cacheflush.h>
@@ -71,6 +72,13 @@ int cpu_suspend(unsigned long arg, int (
 	local_dbg_save(flags);
 
 	/*
+	 * Function graph tracer state gets incosistent when the kernel
+	 * calls functions that never return (aka suspend finishers) hence
+	 * disable graph tracing during their execution.
+	 */
+	pause_graph_tracing();
+
+	/*
 	 * mm context saved on the stack, it will be restored when
 	 * the cpu comes out of reset through the identity mapped
 	 * page tables, so that the thread address space is properly
@@ -111,6 +119,8 @@ int cpu_suspend(unsigned long arg, int (
 			hw_breakpoint_restore(NULL);
 	}
 
+	unpause_graph_tracing();
+
 	/*
 	 * Restore pstate flags. OS lock and mdscr have been already
 	 * restored, so from this point onwards, debugging is fully


Patches currently in stable-queue which might be from lorenzo.pieralisi@arm.com are

queue-4.1/arm64-kernel-pause-unpause-function-graph-tracer-in-cpu_suspend.patch