[RFC][PATCH] PM: Rework disabling of user mode helpers during suspend/hibernation

["Rafael J. Wysocki" <rjw@sisk.pl>]

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 the resume.
However, this is not an ideal solution, because if any drivers want
to upolad firmware into memory before suspend, they have to use a
PM notifier for this purpose and there is not 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.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 include/linux/kmod.h |    5 +++
 kernel/kmod.c        |   65 +++++++++++++++++++++------------------------------
 kernel/power/disk.c  |   11 ++++++++
 kernel/power/main.c  |    7 +++++
 kernel/power/user.c  |   10 +++++++
 5 files changed, 60 insertions(+), 38 deletions(-)

Index: linux-2.6/kernel/kmod.c
===================================================================
--- linux-2.6.orig/kernel/kmod.c
+++ linux-2.6/kernel/kmod.c
@@ -265,7 +265,7 @@ static void __call_usermodehelper(struct
 	}
 }
 
-#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
@@ -288,39 +288,37 @@ static DECLARE_WAIT_QUEUE_HEAD(running_h
  */
 #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)
@@ -334,18 +332,12 @@ static void helper_unlock(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
@@ -515,5 +507,4 @@ void __init usermodehelper_init(void)
 {
 	khelper_wq = create_singlethread_workqueue("khelper");
 	BUG_ON(!khelper_wq);
-	register_pm_notifier_callback();
 }
Index: linux-2.6/include/linux/kmod.h
===================================================================
--- linux-2.6.orig/include/linux/kmod.h
+++ linux-2.6/include/linux/kmod.h
@@ -99,4 +99,9 @@ struct file;
 extern int call_usermodehelper_pipe(char *path, char *argv[], char *envp[],
 				    struct file **filp);
 
+#ifdef CONFIG_PM_SLEEP
+extern int usermodehelper_disable(void);
+extern void usermodehelper_enable(void);
+#endif
+
 #endif /* __LINUX_KMOD_H__ */
Index: linux-2.6/kernel/power/main.c
===================================================================
--- linux-2.6.orig/kernel/power/main.c
+++ linux-2.6/kernel/power/main.c
@@ -21,6 +21,7 @@
 #include <linux/freezer.h>
 #include <linux/vmstat.h>
 #include <linux/syscalls.h>
+#include <linux/kmod.h>
 
 #include "power.h"
 
@@ -236,6 +237,10 @@ static int suspend_prepare(void)
 	if (error)
 		goto Finish;
 
+	error = usermodehelper_disable();
+	if (error)
+		goto Finish;
+
 	if (suspend_freeze_processes()) {
 		error = -EAGAIN;
 		goto Thaw;
@@ -255,6 +260,7 @@ static int suspend_prepare(void)
 
  Thaw:
 	suspend_thaw_processes();
+	usermodehelper_enable();
  Finish:
 	pm_notifier_call_chain(PM_POST_SUSPEND);
 	pm_restore_console();
@@ -373,6 +379,7 @@ int suspend_devices_and_enter(suspend_st
 static void suspend_finish(void)
 {
 	suspend_thaw_processes();
+	usermodehelper_enable();
 	pm_notifier_call_chain(PM_POST_SUSPEND);
 	pm_restore_console();
 }
Index: linux-2.6/kernel/power/disk.c
===================================================================
--- linux-2.6.orig/kernel/power/disk.c
+++ linux-2.6/kernel/power/disk.c
@@ -21,6 +21,7 @@
 #include <linux/console.h>
 #include <linux/cpu.h>
 #include <linux/freezer.h>
+#include <linux/kmod.h>
 
 #include "power.h"
 
@@ -513,6 +514,10 @@ int hibernate(void)
 	if (error)
 		goto Exit;
 
+	error = usermodehelper_disable();
+	if (error)
+		goto Exit;
+
 	/* Allocate memory management structures */
 	error = create_basic_memory_bitmaps();
 	if (error)
@@ -551,6 +556,7 @@ int hibernate(void)
 	thaw_processes();
  Finish:
 	free_basic_memory_bitmaps();
+	usermodehelper_enable();
  Exit:
 	pm_notifier_call_chain(PM_POST_HIBERNATION);
 	pm_restore_console();
@@ -627,6 +633,10 @@ static int software_resume(void)
 	if (error)
 		goto Finish;
 
+	error = usermodehelper_disable();
+	if (error)
+		goto Finish;
+
 	error = create_basic_memory_bitmaps();
 	if (error)
 		goto Finish;
@@ -649,6 +659,7 @@ static int software_resume(void)
 	thaw_processes();
  Done:
 	free_basic_memory_bitmaps();
+	usermodehelper_enable();
  Finish:
 	pm_notifier_call_chain(PM_POST_RESTORE);
 	pm_restore_console();
Index: linux-2.6/kernel/power/user.c
===================================================================
--- linux-2.6.orig/kernel/power/user.c
+++ linux-2.6/kernel/power/user.c
@@ -212,13 +212,20 @@ static long snapshot_ioctl(struct file *
 	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;
@@ -227,6 +234,7 @@ static long snapshot_ioctl(struct file *
 		if (!data->frozen || data->ready)
 			break;
 		thaw_processes();
+		usermodehelper_enable();
 		data->frozen = 0;
 		break;