[PATCH] ARM: ftrace: pause/unpause function graph tracer in cpu_suspend()

[Louis Wang]

From: "louis.wang1" <louis.wang1 at unisoc.com>

Enabling function_graph tracer on ARM causes kernel panic, because the
function graph tracer updates the "return address" of a function in order
to insert a trace callback on function exit, it saves the function's
original return address in a return trace stack, but cpu_suspend() may not
return through the normal return path.

cpu_suspend() will resume directly via the cpu_resume path, but the return
trace stack has been set-up by the subfunctions of cpu_suspend(), which
makes the "return address" inconsistent with cpu_suspend().

This patch refers to Commit de818bd4522c40ea02a81b387d2fa86f989c9623
("arm64: kernel: pause/unpause function graph tracer in cpu_suspend()"),
fixes the issue by pausing/resuming the function graph tracer on the thread
executing cpu_suspend(), 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.

Signed-off-by: louis.wang1 <louis.wang1 at unisoc.com>
---
 arch/arm/kernel/suspend.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/suspend.c b/arch/arm/kernel/suspend.c
index 24bd205..43f0a3e 100644
--- a/arch/arm/kernel/suspend.c
+++ b/arch/arm/kernel/suspend.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <linux/ftrace.h>
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/mm_types.h>
@@ -26,12 +27,22 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 		return -EINVAL;
 
 	/*
+	 * 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();
+
+	/*
 	 * Provide a temporary page table with an identity mapping for
 	 * the MMU-enable code, required for resuming.  On successful
 	 * resume (indicated by a zero return code), we need to switch
 	 * back to the correct page tables.
 	 */
 	ret = __cpu_suspend(arg, fn, __mpidr);
+
+	unpause_graph_tracing();
+
 	if (ret == 0) {
 		cpu_switch_mm(mm->pgd, mm);
 		local_flush_bp_all();
@@ -45,7 +56,13 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 {
 	u32 __mpidr = cpu_logical_map(smp_processor_id());
-	return __cpu_suspend(arg, fn, __mpidr);
+	int ret;
+
+	pause_graph_tracing();
+	ret = __cpu_suspend(arg, fn, __mpidr);
+	unpause_graph_tracing();
+
+	return ret;
 }
 #define	idmap_pgd	NULL
 #endif
-- 
2.7.4