PM: disable usermode helper before hibernation and suspend

Use a hibernation and suspend notifier to disable the user mode helper before
a hibernation/suspend and enable it after the operation.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Nigel Cunningham <nigel@nigel.suspend2.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/kmod.c

@@ -33,12 +33,22 @@
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/resource.h>
+#include <linux/notifier.h>
+#include <linux/suspend.h>
 #include <asm/uaccess.h>
 
 extern int max_threads;
 
 static struct workqueue_struct *khelper_wq;
 
+/*
+ * If set, both call_usermodehelper_keys() and call_usermodehelper_pipe() exit
+ * immediately returning -EBUSY.  Used for preventing user land processes from
+ * being created after the user land has been frozen during a system-wide
+ * hibernation or suspend operation.
+ */
+static int usermodehelper_disabled;
+
 #ifdef CONFIG_KMOD
 
 /*
@@ -265,6 +275,24 @@ static void __call_usermodehelper(struct work_struct *work)
 	}
 }
 
+static int usermodehelper_pm_callback(struct notifier_block *nfb,
+					unsigned long action,
+					void *ignored)
+{
+	switch (action) {
+	case PM_HIBERNATION_PREPARE:
+	case PM_SUSPEND_PREPARE:
+		usermodehelper_disabled = 1;
+		return NOTIFY_OK;
+	case PM_POST_HIBERNATION:
+	case PM_POST_SUSPEND:
+		usermodehelper_disabled = 0;
+		return NOTIFY_OK;
+	}
+
+	return NOTIFY_DONE;
+}
+
 /**
  * call_usermodehelper_setup - prepare to call a usermode helper
  * @path - path to usermode executable
@@ -374,7 +402,7 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info,
 		goto out;
 	}
 
-	if (!khelper_wq) {
+	if (!khelper_wq || usermodehelper_disabled) {
 		retval = -EBUSY;
 		goto out;
 	}
@@ -431,4 +459,5 @@ void __init usermodehelper_init(void)
 {
 	khelper_wq = create_singlethread_workqueue("khelper");
 	BUG_ON(!khelper_wq);
+	pm_notifier(usermodehelper_pm_callback, 0);
 }