PM / Sleep: increase ftrace coverage in suspend/resume

Change where ftrace is disabled and re-enabled during system
suspend/resume to allow tracing of device driver pm callbacks.
Ftrace will now be turned off when suspend reaches
disable_nonboot_cpus() instead of at the very beginning of system
suspend.

Ftrace was disabled during suspend/resume back in 2008 by
Steven Rostedt as he discovered there was a conflict in the
enable_nonboot_cpus() call (see commit f42ac38 "ftrace: disable
tracing for suspend to ram").  This change preserves his fix by
disabling ftrace, but only at the function where it is known
to cause problems.

The new change allows tracing of the device level code for better
debug.

[rjw: Changelog]
Signed-off-by: Todd Brandt <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>

kernel/power/suspend.c

@@ -210,6 +210,7 @@ static int suspend_enter(suspend_state_t state, bool *wakeup)
 		goto Platform_wake;
 	}
 
+	ftrace_stop();
 	error = disable_nonboot_cpus();
 	if (error || suspend_test(TEST_CPUS))
 		goto Enable_cpus;
@@ -232,6 +233,7 @@ static int suspend_enter(suspend_state_t state, bool *wakeup)
 
  Enable_cpus:
 	enable_nonboot_cpus();
+	ftrace_start();
 
  Platform_wake:
 	if (need_suspend_ops(state) && suspend_ops->wake)
@@ -265,7 +267,6 @@ int suspend_devices_and_enter(suspend_state_t state)
 			goto Close;
 	}
 	suspend_console();
-	ftrace_stop();
 	suspend_test_start();
 	error = dpm_suspend_start(PMSG_SUSPEND);
 	if (error) {
@@ -285,7 +286,6 @@ int suspend_devices_and_enter(suspend_state_t state)
 	suspend_test_start();
 	dpm_resume_end(PMSG_RESUME);
 	suspend_test_finish("resume devices");
-	ftrace_start();
 	resume_console();
  Close:
 	if (need_suspend_ops(state) && suspend_ops->end)