pm: rework disabling of user mode helpers during suspend/hibernation

We currently use a PM notifier to disable user mode helpers before suspend
and hibernation and to re-enable them during resume. However, this is not
an ideal solution, because if any drivers want to upload firmware into
memory before suspend, they have to use a PM notifier for this purpose and
there is no guarantee that the ordering of PM notifiers will be as
expected (ie. the notifier that disables user mode helpers has to be run
after the driver's notifier used for uploading the firmware).

For this reason, it seems better to move the disabling and enabling of
user mode helpers to separate functions that will be called by the PM core
as necessary.

[[e-mail]: remove unneeded ifdefs]
Signed-off-by: Rafael J. Wysocki <[e-mail]>
Cc: Alan Stern <[e-mail]>
Acked-by: Pavel Machek <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/kmod.h

···
 extern int call_usermodehelper_pipe(char *path, char *argv[], char *envp[],
 				    struct file **filp);
 
+extern int usermodehelper_disable(void);
+extern void usermodehelper_enable(void);
+
 #endif /* __LINUX_KMOD_H__ */

kernel/kmod.c

···
 	}
 }
 
-#ifdef CONFIG_PM
+#ifdef CONFIG_PM_SLEEP
 /*
  * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
  * (used for preventing user land processes from being created after the user
···
  */
 #define RUNNING_HELPERS_TIMEOUT	(5 * HZ)
 
-static int usermodehelper_pm_callback(struct notifier_block *nfb,
-					unsigned long action,
-					void *ignored)
+/**
+ * usermodehelper_disable - prevent new helpers from being started
+ */
+int usermodehelper_disable(void)
 {
 	long retval;
 
-	switch (action) {
-	case PM_HIBERNATION_PREPARE:
-	case PM_SUSPEND_PREPARE:
-		usermodehelper_disabled = 1;
-		smp_mb();
-		/*
-		 * From now on call_usermodehelper_exec() won't start any new
-		 * helpers, so it is sufficient if running_helpers turns out to
-		 * be zero at one point (it may be increased later, but that
-		 * doesn't matter).
-		 */
-		retval = wait_event_timeout(running_helpers_waitq,
+	usermodehelper_disabled = 1;
+	smp_mb();
+	/*
+	 * From now on call_usermodehelper_exec() won't start any new
+	 * helpers, so it is sufficient if running_helpers turns out to
+	 * be zero at one point (it may be increased later, but that
+	 * doesn't matter).
+	 */
+	retval = wait_event_timeout(running_helpers_waitq,
 					atomic_read(&running_helpers) == 0,
 					RUNNING_HELPERS_TIMEOUT);
-		if (retval) {
-			return NOTIFY_OK;
-		} else {
-			usermodehelper_disabled = 0;
-			return NOTIFY_BAD;
-		}
-	case PM_POST_HIBERNATION:
-	case PM_POST_SUSPEND:
-		usermodehelper_disabled = 0;
-		return NOTIFY_OK;
-	}
+	if (retval)
+		return 0;
 
-	return NOTIFY_DONE;
+	usermodehelper_disabled = 0;
+	return -EAGAIN;
+}
+
+/**
+ * usermodehelper_enable - allow new helpers to be started again
+ */
+void usermodehelper_enable(void)
+{
+	usermodehelper_disabled = 0;
 }
 
 static void helper_lock(void)
···
 	if (atomic_dec_and_test(&running_helpers))
 		wake_up(&running_helpers_waitq);
 }
-
-static void register_pm_notifier_callback(void)
-{
-	pm_notifier(usermodehelper_pm_callback, 0);
-}
-#else /* CONFIG_PM */
+#else /* CONFIG_PM_SLEEP */
 #define usermodehelper_disabled	0
 
 static inline void helper_lock(void) {}
 static inline void helper_unlock(void) {}
-static inline void register_pm_notifier_callback(void) {}
-#endif /* CONFIG_PM */
+#endif /* CONFIG_PM_SLEEP */
 
 /**
  * call_usermodehelper_setup - prepare to call a usermode helper
···
 {
 	khelper_wq = create_singlethread_workqueue("khelper");
 	BUG_ON(!khelper_wq);
-	register_pm_notifier_callback();
 }

kernel/power/disk.c

···
 #include <linux/reboot.h>
 #include <linux/string.h>
 #include <linux/device.h>
+#include <linux/kmod.h>
 #include <linux/delay.h>
 #include <linux/fs.h>
 #include <linux/mount.h>
···
 	if (error)
 		goto Exit;
 
+	error = usermodehelper_disable();
+	if (error)
+		goto Exit;
+
 	/* Allocate memory management structures */
 	error = create_basic_memory_bitmaps();
 	if (error)
···
 	thaw_processes();
  Finish:
 	free_basic_memory_bitmaps();
+	usermodehelper_enable();
  Exit:
 	pm_notifier_call_chain(PM_POST_HIBERNATION);
 	pm_restore_console();
···
 	if (error)
 		goto Finish;
 
+	error = usermodehelper_disable();
+	if (error)
+		goto Finish;
+
 	error = create_basic_memory_bitmaps();
 	if (error)
 		goto Finish;
···
 	thaw_processes();
  Done:
 	free_basic_memory_bitmaps();
+	usermodehelper_enable();
  Finish:
 	pm_notifier_call_chain(PM_POST_RESTORE);
 	pm_restore_console();

kernel/power/main.c

···
 #include <linux/string.h>
 #include <linux/delay.h>
 #include <linux/errno.h>
+#include <linux/kmod.h>
 #include <linux/init.h>
 #include <linux/console.h>
 #include <linux/cpu.h>
···
 	if (error)
 		goto Finish;
 
+	error = usermodehelper_disable();
+	if (error)
+		goto Finish;
+
 	if (suspend_freeze_processes()) {
 		error = -EAGAIN;
 		goto Thaw;
···
 
  Thaw:
 	suspend_thaw_processes();
+	usermodehelper_enable();
  Finish:
 	pm_notifier_call_chain(PM_POST_SUSPEND);
 	pm_restore_console();
···
 static void suspend_finish(void)
 {
 	suspend_thaw_processes();
+	usermodehelper_enable();
 	pm_notifier_call_chain(PM_POST_SUSPEND);
 	pm_restore_console();
 }

kernel/power/user.c

···
 	case SNAPSHOT_FREEZE:
 		if (data->frozen)
 			break;
+
 		printk("Syncing filesystems ... ");
 		sys_sync();
 		printk("done.\n");
 
-		error = freeze_processes();
+		error = usermodehelper_disable();
 		if (error)
+			break;
+
+		error = freeze_processes();
+		if (error) {
 			thaw_processes();
+			usermodehelper_enable();
+		}
 		if (!error)
 			data->frozen = 1;
 		break;
···
 		if (!data->frozen || data->ready)
 			break;
 		thaw_processes();
+		usermodehelper_enable();
 		data->frozen = 0;
 		break;