[PATCH -mm 0/2] PM: Hibernation and suspend notifiers

[PATCH -mm 0/2] PM: Hibernation and suspend notifiers

[Rafael J. Wysocki]

Hi,

The first of the following two patches introduces hibernation and suspend
notifiers that can be used by subsystems to perform tasks related to suspend
and/or hibernation that cannot be done from device drivers' .suspend() and
.resume() callbacks.

The second one uses the notifiers to disable the user mode helper functionality
before a hibernation/suspend.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth

[PATCH -mm 1/2] PM: Introduce hibernation and suspend notifiers

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rjw@sisk.pl>

Make it possible to register hibernation and suspend notifiers, so that
subsystems can perform hibernation-related or suspend-related operations that
should not be carried out by device drivers' .suspend() and .resume() routines.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
---
 Documentation/power/notifiers.txt |   50 ++++++++++++++++++++++++++++++++++++++
 include/linux/notifier.h          |    6 ++++
 include/linux/suspend.h           |   37 +++++++++++++++++++++++++---
 kernel/power/disk.c               |   16 +++++++++---
 kernel/power/main.c               |    9 ++++++
 kernel/power/power.h              |   10 +++++++
 kernel/power/user.c               |   11 ++++++--
 7 files changed, 129 insertions(+), 10 deletions(-)

Index: linux-2.6.22-rc3/include/linux/suspend.h
===================================================================
--- linux-2.6.22-rc3.orig/include/linux/suspend.h	2007-05-31 00:00:38.000000000 +0200
+++ linux-2.6.22-rc3/include/linux/suspend.h	2007-06-01 22:55:01.000000000 +0200
@@ -54,7 +54,8 @@ struct hibernation_ops {
 	void (*restore_cleanup)(void);
 };
 
-#if defined(CONFIG_PM) && defined(CONFIG_SOFTWARE_SUSPEND)
+#ifdef CONFIG_PM
+#ifdef CONFIG_SOFTWARE_SUSPEND
 /* kernel/power/snapshot.c */
 extern void __register_nosave_region(unsigned long b, unsigned long e, int km);
 static inline void register_nosave_region(unsigned long b, unsigned long e)
@@ -72,7 +73,7 @@ extern unsigned long get_safe_page(gfp_t
 
 extern void hibernation_set_ops(struct hibernation_ops *ops);
 extern int hibernate(void);
-#else
+#else /* CONFIG_SOFTWARE_SUSPEND */
 static inline void register_nosave_region(unsigned long b, unsigned long e) {}
 static inline void register_nosave_region_late(unsigned long b, unsigned long e) {}
 static inline int swsusp_page_is_forbidden(struct page *p) { return 0; }
@@ -81,7 +82,7 @@ static inline void swsusp_unset_page_fre
 
 static inline void hibernation_set_ops(struct hibernation_ops *ops) {}
 static inline int hibernate(void) { return -ENOSYS; }
-#endif /* defined(CONFIG_PM) && defined(CONFIG_SOFTWARE_SUSPEND) */
+#endif /* CONFIG_SOFTWARE_SUSPEND */
 
 void save_processor_state(void);
 void restore_processor_state(void);
@@ -89,4 +90,34 @@ struct saved_context;
 void __save_processor_state(struct saved_context *ctxt);
 void __restore_processor_state(struct saved_context *ctxt);
 
+/* kernel/power/main.c */
+extern struct blocking_notifier_head pm_chain_head;
+
+static inline int register_pm_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&pm_chain_head, nb);
+}
+
+static inline int unregister_pm_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&pm_chain_head, nb);
+}
+
+#define pm_notifier(fn, pri) {				\
+	static struct notifier_block fn##_nb =			\
+		{ .notifier_call = fn, .priority = pri };	\
+	register_pm_notifier(&fn##_nb);			\
+}
+#else /* CONFIG_PM */
+static inline int register_pm_notifier(struct notifier_block *nb) {
+	return 0;
+}
+
+static inline int unregister_pm_notifier(struct notifier_block *nb) {
+	return 0;
+}
+
+#define pm_notifier(fn, pri)	do { (void)(fn); } while (0)
+#endif /* CONFIG_PM */
+
 #endif /* _LINUX_SWSUSP_H */
Index: linux-2.6.22-rc3/kernel/power/power.h
===================================================================
--- linux-2.6.22-rc3.orig/kernel/power/power.h	2007-05-31 00:00:38.000000000 +0200
+++ linux-2.6.22-rc3/kernel/power/power.h	2007-06-01 22:55:01.000000000 +0200
@@ -173,5 +173,15 @@ extern void swsusp_close(void);
 extern int suspend_enter(suspend_state_t state);
 
 struct timeval;
+/* kernel/power/swsusp.c */
 extern void swsusp_show_speed(struct timeval *, struct timeval *,
 				unsigned int, char *);
+
+/* kernel/power/main.c */
+extern struct blocking_notifier_head pm_chain_head;
+
+static inline int pm_notifier_call_chain(unsigned long val)
+{
+	return (blocking_notifier_call_chain(&pm_chain_head, val, NULL)
+			== NOTIFY_BAD) ? -EINVAL : 0;
+}
Index: linux-2.6.22-rc3/include/linux/notifier.h
===================================================================
--- linux-2.6.22-rc3.orig/include/linux/notifier.h	2007-05-31 00:00:38.000000000 +0200
+++ linux-2.6.22-rc3/include/linux/notifier.h	2007-06-01 23:01:38.000000000 +0200
@@ -209,5 +209,11 @@ extern int __srcu_notifier_call_chain(st
 #define CPU_DOWN_FAILED_FROZEN	(CPU_DOWN_FAILED | CPU_TASKS_FROZEN)
 #define CPU_DEAD_FROZEN		(CPU_DEAD | CPU_TASKS_FROZEN)
 
+/* Hibernation and suspend events */
+#define PM_HIBERNATION_PREPARE	0x0001 /* Going to hibernate */
+#define PM_POST_HIBERNATION	0x0002 /* Hibernation finished */
+#define PM_SUSPEND_PREPARE	0x0003 /* Going to suspend the system */
+#define PM_POST_SUSPEND		0x0004 /* Suspend finished */
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */
Index: linux-2.6.22-rc3/kernel/power/disk.c
===================================================================
--- linux-2.6.22-rc3.orig/kernel/power/disk.c	2007-05-31 00:00:38.000000000 +0200
+++ linux-2.6.22-rc3/kernel/power/disk.c	2007-06-01 23:05:11.000000000 +0200
@@ -281,9 +281,16 @@ int hibernate(void)
 {
 	int error;
 
+	mutex_lock(&pm_mutex);
 	/* The snapshot device should not be opened while we're running */
-	if (!atomic_add_unless(&snapshot_device_available, -1, 0))
-		return -EBUSY;
+	if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
+		error = -EBUSY;
+		goto Unlock;
+	}
+
+	error = pm_notifier_call_chain(PM_HIBERNATION_PREPARE);
+	if (error)
+		goto Exit;
 
 	/* Allocate memory management structures */
 	error = create_basic_memory_bitmaps();
@@ -294,7 +301,6 @@ int hibernate(void)
 	if (error)
 		goto Finish;
 
-	mutex_lock(&pm_mutex);
 	if (hibernation_mode == HIBERNATION_TESTPROC) {
 		printk("swsusp debug: Waiting for 5 seconds.\n");
 		mdelay(5000);
@@ -316,12 +322,14 @@ int hibernate(void)
 		swsusp_free();
 	}
  Thaw:
-	mutex_unlock(&pm_mutex);
 	unprepare_processes();
  Finish:
 	free_basic_memory_bitmaps();
  Exit:
+	pm_notifier_call_chain(PM_POST_HIBERNATION);
 	atomic_inc(&snapshot_device_available);
+ Unlock:
+	mutex_unlock(&pm_mutex);
 	return error;
 }
 
Index: linux-2.6.22-rc3/kernel/power/main.c
===================================================================
--- linux-2.6.22-rc3.orig/kernel/power/main.c	2007-05-31 00:00:38.000000000 +0200
+++ linux-2.6.22-rc3/kernel/power/main.c	2007-06-01 23:08:43.000000000 +0200
@@ -24,6 +24,8 @@
 
 #include "power.h"
 
+BLOCKING_NOTIFIER_HEAD(pm_chain_head);
+
 /*This is just an arbitrary number */
 #define FREE_PAGE_NUMBER (100)
 
@@ -82,6 +84,10 @@ static int suspend_prepare(suspend_state
 	if (!pm_ops || !pm_ops->enter)
 		return -EPERM;
 
+	error = pm_notifier_call_chain(PM_SUSPEND_PREPARE);
+	if (error)
+		goto Finish;
+
 	pm_prepare_console();
 
 	if (freeze_processes()) {
@@ -124,6 +130,8 @@ static int suspend_prepare(suspend_state
  Thaw:
 	thaw_processes();
 	pm_restore_console();
+ Finish:
+	pm_notifier_call_chain(PM_POST_SUSPEND);
 	return error;
 }
 
@@ -175,6 +183,7 @@ static void suspend_finish(suspend_state
 	resume_console();
 	thaw_processes();
 	pm_restore_console();
+	pm_notifier_call_chain(PM_POST_SUSPEND);
 }
 
 
Index: linux-2.6.22-rc3/kernel/power/user.c
===================================================================
--- linux-2.6.22-rc3.orig/kernel/power/user.c	2007-05-31 00:00:38.000000000 +0200
+++ linux-2.6.22-rc3/kernel/power/user.c	2007-06-01 23:15:58.000000000 +0200
@@ -149,10 +149,14 @@ static int snapshot_ioctl(struct inode *
 		if (data->frozen)
 			break;
 		mutex_lock(&pm_mutex);
-		if (freeze_processes()) {
-			thaw_processes();
-			error = -EBUSY;
+		error = pm_notifier_call_chain(PM_HIBERNATION_PREPARE);
+		if (!error) {
+			error = freeze_processes();
+			if (error)
+				thaw_processes();
 		}
+		if (error)
+			pm_notifier_call_chain(PM_POST_HIBERNATION);
 		mutex_unlock(&pm_mutex);
 		if (!error)
 			data->frozen = 1;
@@ -163,6 +167,7 @@ static int snapshot_ioctl(struct inode *
 			break;
 		mutex_lock(&pm_mutex);
 		thaw_processes();
+		pm_notifier_call_chain(PM_POST_HIBERNATION);
 		mutex_unlock(&pm_mutex);
 		data->frozen = 0;
 		break;
Index: linux-2.6.22-rc3/Documentation/power/notifiers.txt
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.22-rc3/Documentation/power/notifiers.txt	2007-06-01 23:14:59.000000000 +0200
@@ -0,0 +1,50 @@
+Suspend notifiers
+	(C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL
+
+There are some operations that device drivers may want to carry out in their
+.suspend() routines, but shouldn't, because they can cause the hibernation or
+suspend to fail. For example, a driver may want to allocate a substantial amount
+of memory (like 50 MB) in .suspend(), but that shouldn't be done after the
+swsusp's memory shrinker has run.
+
+Also, there may be some operations, that subsystems want to carry out before a
+hibernation/suspend or after a restore/resume, requiring the system to be fully
+functional, so the drivers' .suspend() and .resume() routines are not suitable
+for this purpose.  For example, device drivers may want to upload firmware to
+their devices after a restore from a hibernation image, but they cannot do it by
+calling request_firmware() from their .resume() routines (user land processes
+are frozen at this point).  The solution may be to load the firmware into
+memory before processes are frozen and upload it from there in the .resume()
+routine.  Of course, a hibernation notifier may be used for this purpose.
+
+The subsystems that have such needs can register suspend notifiers that will be
+called upon the following events by the suspend core:
+
+PM_HIBERNATION_PREPARE	The system is going to hibernate or suspend, tasks will
+			be frozen immediately.
+
+PM_POST_HIBERNATION	The system memory state has been restored from a
+			hibernation image or an error occured during the
+			hibernation.  Device drivers' .resume() callbacks have
+			been executed and tasks have been thawed.
+
+PM_SUSPEND_PREPARE	The system is preparing for a suspend.
+
+PM_POST_SUSPEND		The system has just resumed or an error occured during
+			the suspend.	Device drivers' .resume() callbacks have
+			been executed and tasks have been thawed.
+
+It is generally assumed that whatever the notifiers do for
+PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION.  Analogously,
+operations performed for PM_SUSPEND_PREPARE should be reversed for
+PM_POST_SUSPEND.  Additionally, all of the notifiers are called for
+PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and
+all of the notifiers are called for PM_POST_SUSPEND if one of them fails for
+PM_SUSPEND_PREPARE.
+
+The hibernation and suspend notifiers are called with pm_mutex held.  They are
+defined in the usual way, but their last argument is meaningless (it is always
+NULL).  To register and/or unregister a suspend notifier use the functions
+register_pm_notifier() and unregister_pm_notifier(), respectively, defined in
+include/linux/suspend.h .  If you don't need to unregister the notifier, you can
+also use the pm_notifier() macro defined in include/linux/suspend.h .

[PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rjw@sisk.pl>

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

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
---
 kernel/kmod.c |   33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

Index: linux-2.6.22-rc3/kernel/kmod.c
===================================================================
--- linux-2.6.22-rc3.orig/kernel/kmod.c	2007-05-31 00:00:37.000000000 +0200
+++ linux-2.6.22-rc3/kernel/kmod.c	2007-06-02 00:01:47.000000000 +0200
@@ -33,6 +33,8 @@
 #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;
@@ -46,6 +48,14 @@ static struct workqueue_struct *khelper_
 */
 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
 
+/*
+ * 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;
+
 /**
  * request_module - try to load a kernel module
  * @fmt:     printf style format string for the name of the module
@@ -251,6 +261,24 @@ static void __call_usermodehelper(struct
 		complete(sub_info->complete);
 }
 
+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_keys - start a usermode application
  * @path: pathname for the application
@@ -276,7 +304,7 @@ int call_usermodehelper_keys(char *path,
 	struct subprocess_info *sub_info;
 	int retval;
 
-	if (!khelper_wq)
+	if (!khelper_wq || usermodehelper_disabled)
 		return -EBUSY;
 
 	if (path[0] == '\0')
@@ -319,7 +347,7 @@ int call_usermodehelper_pipe(char *path,
 	};
 	struct file *f;
 
-	if (!khelper_wq)
+	if (!khelper_wq || usermodehelper_disabled)
 		return -EBUSY;
 
 	if (path[0] == '\0')
@@ -347,4 +375,5 @@ void __init usermodehelper_init(void)
 {
 	khelper_wq = create_singlethread_workqueue("khelper");
 	BUG_ON(!khelper_wq);
+	pm_notifier(usermodehelper_pm_callback, 0);
 }

Re: [PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend

[Nigel Cunningham]

[-- Attachment #1: Type: text/plain, Size: 27 bytes --]

Ack.

Regards,

Nigel

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 189 bytes --]

Re: [PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend

[Uli Luckas]

On Monday, 4. June 2007, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@sisk.pl>
>
> Use a hibernation and suspend notifier to disable the user mode helper
> before a hibernation/suspend and enable it after the operation.
>
Hi Rafael,
I have a couple of questions, regarding this patch ...
> -	if (!khelper_wq)
> +	if (!khelper_wq || usermodehelper_disabled)
>  		return -EBUSY;
1) how about not returning -EBUSY here, if (wait == UMH_NO_WAIT)?
2) how does your patch prevent wait_for_completion(&done) to hang during
   freezing if usermodehelper_pm_callback is called _after_ the above check?

Regards
Uli

Re: [PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend

[Rafael J. Wysocki]

On Friday, 15 June 2007 15:08, Uli Luckas wrote:
> On Monday, 4. June 2007, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@sisk.pl>
> >
> > Use a hibernation and suspend notifier to disable the user mode helper
> > before a hibernation/suspend and enable it after the operation.
> >
> Hi Rafael,
> I have a couple of questions, regarding this patch ...
> > -	if (!khelper_wq)
> > +	if (!khelper_wq || usermodehelper_disabled)
> >  		return -EBUSY;
> 1) how about not returning -EBUSY here, if (wait == UMH_NO_WAIT)?

Yes, this would make sense.

> 2) how does your patch prevent wait_for_completion(&done) to hang during
>    freezing if usermodehelper_pm_callback is called _after_ the above check?

It doesn't.  Once the helper is running, we can't distinguish it from any other
user land process.

Still, it narrows the window quite a bit.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth

Re: [PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend

[Rafael J. Wysocki]

On Friday, 15 June 2007 23:36, Rafael J. Wysocki wrote:
> On Friday, 15 June 2007 15:08, Uli Luckas wrote:
> > On Monday, 4. June 2007, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rjw@sisk.pl>
> > >
> > > Use a hibernation and suspend notifier to disable the user mode helper
> > > before a hibernation/suspend and enable it after the operation.
> > >
> > Hi Rafael,
> > I have a couple of questions, regarding this patch ...
> > > -	if (!khelper_wq)
> > > +	if (!khelper_wq || usermodehelper_disabled)
> > >  		return -EBUSY;
> > 1) how about not returning -EBUSY here, if (wait == UMH_NO_WAIT)?
> 
> Yes, this would make sense.

I know why I didn't do that from the start: my patch was against -rc4 and
UMH_NO_WAIT is mm-only.

> > 2) how does your patch prevent wait_for_completion(&done) to hang during
> >    freezing if usermodehelper_pm_callback is called _after_ the above check?
> 
> It doesn't.  Once the helper is running, we can't distinguish it from any other
> user land process.
> 
> Still, it narrows the window quite a bit.

Okay, I think we can help it a bit.  Please tell me what you think of the
following patch (on top of 2.6.22-rc4-mm2).

Greetings,
Rafael


Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 kernel/kmod.c |   24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

Index: linux-2.6.22-rc4-mm2/kernel/kmod.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/kernel/kmod.c
+++ linux-2.6.22-rc4-mm2/kernel/kmod.c
@@ -49,6 +49,15 @@ static struct workqueue_struct *khelper_
  */
 static int usermodehelper_disabled;
 
+/* Number of helpers running */
+static atomic_t running_helpers = ATOMIC_INIT(0);
+
+/*
+ * Time to wait for running_helpers to become zero before the setting of
+ * usermodehelper_disabled in usermodehelper_pm_callback() fails
+ */
+#define RUNNING_HELPERS_TIMEOUT	(5 * HZ)
+
 #ifdef CONFIG_KMOD
 
 /*
@@ -279,11 +288,20 @@ static int usermodehelper_pm_callback(st
 					unsigned long action,
 					void *ignored)
 {
+	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(waiting);
+
 	switch (action) {
 	case PM_HIBERNATION_PREPARE:
 	case PM_SUSPEND_PREPARE:
 		usermodehelper_disabled = 1;
-		return NOTIFY_OK;
+		wait_event_timeout(waiting, atomic_read(&running_helpers) == 0,
+					RUNNING_HELPERS_TIMEOUT);
+		if (atomic_read(&running_helpers) == 0) {
+			return NOTIFY_OK;
+		} else {
+			usermodehelper_disabled = 0;
+			return NOTIFY_BAD;
+		}
 	case PM_POST_HIBERNATION:
 	case PM_POST_SUSPEND:
 		usermodehelper_disabled = 0;
@@ -397,12 +415,13 @@ int call_usermodehelper_exec(struct subp
 	DECLARE_COMPLETION_ONSTACK(done);
 	int retval;
 
+	atomic_inc(&running_helpers);
 	if (sub_info->path[0] == '\0') {
 		retval = 0;
 		goto out;
 	}
 
-	if (!khelper_wq || usermodehelper_disabled) {
+	if (!khelper_wq || (wait != UMH_NO_WAIT && usermodehelper_disabled)) {
 		retval = -EBUSY;
 		goto out;
 	}
@@ -418,6 +437,7 @@ int call_usermodehelper_exec(struct subp
 
   out:
 	call_usermodehelper_freeinfo(sub_info);
+	atomic_dec(&running_helpers);
 	return retval;
 }
 EXPORT_SYMBOL(call_usermodehelper_exec);

Re: [PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend

[Uli Luckas]

On Sunday, 17. June 2007, you wrote:
> On Friday, 15 June 2007 23:36, Rafael J. Wysocki wrote:
> > On Friday, 15 June 2007 15:08, Uli Luckas wrote:
> > > On Monday, 4. June 2007, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rjw@sisk.pl>
> > > >
> > > > Use a hibernation and suspend notifier to disable the user mode
> > > > helper before a hibernation/suspend and enable it after the
> > > > operation.
> > >
> > > Hi Rafael,
> > > I have a couple of questions, regarding this patch ...

> > > 2) how does your patch prevent wait_for_completion(&done) to hang
> > > during freezing if usermodehelper_pm_callback is called _after_ the
> > > above check?
> >
> > It doesn't.  Once the helper is running, we can't distinguish it from any
> > other user land process.
> >
> > Still, it narrows the window quite a bit.
>
> Okay, I think we can help it a bit.  Please tell me what you think of the
> following patch (on top of 2.6.22-rc4-mm2).
>
Hi Rafael,
Thanks for your work. I haven't found the time to actually test your patch but 
in general it looks like a valid aproach.
I think there is one problem though. You need to have your wait queue woken up 
when you update (atomic_dec) running_helpers. Otherwise you end up always 
waiting the full RUNNING_HELPERS_TIMEOUT.

> Index: linux-2.6.22-rc4-mm2/kernel/kmod.c
> ===================================================================
> --- linux-2.6.22-rc4-mm2.orig/kernel/kmod.c
> +++ linux-2.6.22-rc4-mm2/kernel/kmod.c
> @@ -49,6 +49,15 @@ static struct workqueue_struct *khelper_
>   */
>  static int usermodehelper_disabled;
>
> +/* Number of helpers running */
> +static atomic_t running_helpers = ATOMIC_INIT(0);
> +
> +/*
> + * Time to wait for running_helpers to become zero before the setting of
> + * usermodehelper_disabled in usermodehelper_pm_callback() fails
> + */
> +#define RUNNING_HELPERS_TIMEOUT	(5 * HZ)
> +
>  #ifdef CONFIG_KMOD
>
>  /*
> @@ -279,11 +288,20 @@ static int usermodehelper_pm_callback(st
>  					unsigned long action,
>  					void *ignored)
>  {
> +	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(waiting);
> +
>  	switch (action) {
>  	case PM_HIBERNATION_PREPARE:
>  	case PM_SUSPEND_PREPARE:
>  		usermodehelper_disabled = 1;
> -		return NOTIFY_OK;
> +		wait_event_timeout(waiting, atomic_read(&running_helpers) == 0,
> +					RUNNING_HELPERS_TIMEOUT);
> +		if (atomic_read(&running_helpers) == 0) {
> +			return NOTIFY_OK;
> +		} else {
> +			usermodehelper_disabled = 0;
> +			return NOTIFY_BAD;
> +		}
>  	case PM_POST_HIBERNATION:
>  	case PM_POST_SUSPEND:
>  		usermodehelper_disabled = 0;
> @@ -397,12 +415,13 @@ int call_usermodehelper_exec(struct subp
>  	DECLARE_COMPLETION_ONSTACK(done);
>  	int retval;
>
> +	atomic_inc(&running_helpers);
>  	if (sub_info->path[0] == '\0') {
>  		retval = 0;
>  		goto out;
>  	}
>
> -	if (!khelper_wq || usermodehelper_disabled) {
> +	if (!khelper_wq || (wait != UMH_NO_WAIT && usermodehelper_disabled)) {
>  		retval = -EBUSY;
>  		goto out;
>  	}
> @@ -418,6 +437,7 @@ int call_usermodehelper_exec(struct subp
>
>    out:
>  	call_usermodehelper_freeinfo(sub_info);
> +	atomic_dec(&running_helpers);
>  	return retval;
>  }
>  EXPORT_SYMBOL(call_usermodehelper_exec);

-- 

------- ROAD ...the handyPC Company - - -  ) ) )

Uli Luckas
Software Development

ROAD GmbH
Bennigsenstr. 14 | 12159 Berlin | Germany
fon: +49 (30) 230069 - 64 | fax: +49 (30) 230069 - 69
url: www.road.de

Amtsgericht Charlottenburg: HRB 96688 B
Managing directors: Hans-Peter Constien, Hubertus von Streit

Re: [PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend

[Rafael J. Wysocki]

On Monday, 18 June 2007 12:51, Uli Luckas wrote:
> On Sunday, 17. June 2007, you wrote:
> > On Friday, 15 June 2007 23:36, Rafael J. Wysocki wrote:
> > > On Friday, 15 June 2007 15:08, Uli Luckas wrote:
> > > > On Monday, 4. June 2007, Rafael J. Wysocki wrote:
> > > > > From: Rafael J. Wysocki <rjw@sisk.pl>
> > > > >
> > > > > Use a hibernation and suspend notifier to disable the user mode
> > > > > helper before a hibernation/suspend and enable it after the
> > > > > operation.
> > > >
> > > > Hi Rafael,
> > > > I have a couple of questions, regarding this patch ...
> 
> > > > 2) how does your patch prevent wait_for_completion(&done) to hang
> > > > during freezing if usermodehelper_pm_callback is called _after_ the
> > > > above check?
> > >
> > > It doesn't.  Once the helper is running, we can't distinguish it from any
> > > other user land process.
> > >
> > > Still, it narrows the window quite a bit.
> >
> > Okay, I think we can help it a bit.  Please tell me what you think of the
> > following patch (on top of 2.6.22-rc4-mm2).
> >
> Hi Rafael,
> Thanks for your work. I haven't found the time to actually test your patch but 
> in general it looks like a valid aproach.
> I think there is one problem though. You need to have your wait queue woken up 
> when you update (atomic_dec) running_helpers. Otherwise you end up always 
> waiting the full RUNNING_HELPERS_TIMEOUT.

Yeah, right.  I tend to forget about obvious things. :-(

Besides, I think that the _pm_callback need not be compiled if CONFIG_PM is
unset.  If you can, please have a look at the next version of the patch (appended).

Greetings,
Rafael


Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 kernel/kmod.c |   76 ++++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 66 insertions(+), 10 deletions(-)

Index: linux-2.6.22-rc4-mm2/kernel/kmod.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/kernel/kmod.c
+++ linux-2.6.22-rc4-mm2/kernel/kmod.c
@@ -41,14 +41,6 @@ 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
 
 /*
@@ -275,6 +267,30 @@ static void __call_usermodehelper(struct
 	}
 }
 
+#ifdef CONFIG_PM
+/*
+ * If set and if call_usermodehelper_exec() is supposed to wait, it will 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;
+
+/* Number of helpers running */
+static atomic_t running_helpers = ATOMIC_INIT(0);
+
+/*
+ * Wait queue head used by usermodehelper_pm_callback() to wait for all running
+ * helpers to finish.
+ */
+static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
+
+/*
+ * Time to wait for running_helpers to become zero before the setting of
+ * usermodehelper_disabled in usermodehelper_pm_callback() fails
+ */
+#define RUNNING_HELPERS_TIMEOUT	(5 * HZ)
+
 static int usermodehelper_pm_callback(struct notifier_block *nfb,
 					unsigned long action,
 					void *ignored)
@@ -283,7 +299,15 @@ static int usermodehelper_pm_callback(st
 	case PM_HIBERNATION_PREPARE:
 	case PM_SUSPEND_PREPARE:
 		usermodehelper_disabled = 1;
-		return NOTIFY_OK;
+		wait_event_timeout(running_helpers_waitq,
+					atomic_read(&running_helpers) == 0,
+					RUNNING_HELPERS_TIMEOUT);
+		if (atomic_read(&running_helpers) == 0) {
+			return NOTIFY_OK;
+		} else {
+			usermodehelper_disabled = 0;
+			return NOTIFY_BAD;
+		}
 	case PM_POST_HIBERNATION:
 	case PM_POST_SUSPEND:
 		usermodehelper_disabled = 0;
@@ -293,6 +317,36 @@ static int usermodehelper_pm_callback(st
 	return NOTIFY_DONE;
 }
 
+static void new_helper(void)
+{
+	atomic_inc(&running_helpers);
+}
+
+static void helper_finished(void)
+{
+	if (atomic_dec_and_test(&running_helpers))
+		wake_up(&running_helpers_waitq);
+}
+
+#else /* CONFIG_PM */
+#define usermodehelper_disabled	0
+
+static inline int usermodehelper_pm_callback(struct notifier_block *nfb,
+						unsigned long action,
+						void *ignored)
+{
+	return 0;
+}
+
+static inline void new_helper(void)
+{
+}
+
+static inline void helper_finished(void)
+{
+}
+#endif /* CONFIG_PM */
+
 /**
  * call_usermodehelper_setup - prepare to call a usermode helper
  * @path - path to usermode executable
@@ -397,12 +451,13 @@ int call_usermodehelper_exec(struct subp
 	DECLARE_COMPLETION_ONSTACK(done);
 	int retval;
 
+	new_helper();
 	if (sub_info->path[0] == '\0') {
 		retval = 0;
 		goto out;
 	}
 
-	if (!khelper_wq || usermodehelper_disabled) {
+	if (!khelper_wq || (wait != UMH_NO_WAIT && usermodehelper_disabled)) {
 		retval = -EBUSY;
 		goto out;
 	}
@@ -418,6 +473,7 @@ int call_usermodehelper_exec(struct subp
 
   out:
 	call_usermodehelper_freeinfo(sub_info);
+	helper_finished();
 	return retval;
 }
 EXPORT_SYMBOL(call_usermodehelper_exec);

Re: [PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend

[Uli Luckas]

On Monday, 18. June 2007, you wrote:
> On Monday, 18 June 2007 12:51, Uli Luckas wrote:
> > On Sunday, 17. June 2007, you wrote:
> > > On Friday, 15 June 2007 23:36, Rafael J. Wysocki wrote:
> > > > On Friday, 15 June 2007 15:08, Uli Luckas wrote:
> > > > > On Monday, 4. June 2007, Rafael J. Wysocki wrote:
> > > > > > From: Rafael J. Wysocki <rjw@sisk.pl>
> > > > > >
> > > > > > Use a hibernation and suspend notifier to disable the user mode
> > > > > > helper before a hibernation/suspend and enable it after the
> > > > > > operation.
> > > > >
> > > > > Hi Rafael,
> > > > > I have a couple of questions, regarding this patch ...
> > > > >
> > > > > 2) how does your patch prevent wait_for_completion(&done) to hang
> > > > > during freezing if usermodehelper_pm_callback is called _after_ the
> > > > > above check?
> > > >
> > > > It doesn't.  Once the helper is running, we can't distinguish it from
> > > > any other user land process.
> > > >
> > > > Still, it narrows the window quite a bit.
> > >
> > > Okay, I think we can help it a bit.  Please tell me what you think of
> > > the following patch (on top of 2.6.22-rc4-mm2).
> >
> > Hi Rafael,
> > Thanks for your work. I haven't found the time to actually test your
> > patch but in general it looks like a valid aproach.
> > I think there is one problem though. You need to have your wait queue
> > woken up when you update (atomic_dec) running_helpers. Otherwise you end
> > up always waiting the full RUNNING_HELPERS_TIMEOUT.
>
> Yeah, right.  I tend to forget about obvious things. :-(
>
Great. As far as I can see, this patch should now fix the situation except 
under heavy load where it would abort the attempted suspend. I can live with 
that and it is a whole lot better than it was before - Thanks.

> Besides, I think that the _pm_callback need not be compiled if CONFIG_PM is
> unset.  
>
Should work but is probably beneath what you intended to do. I'll comment 
further down...

> If you can, please have a look at the next version of the patch 
> (appended).
>
One more topic to keep in mind for the future. None of the callers of 
call_usermode_helper* expect a return value of EBUSY nor do they handle it 
correctly. If auto loading of a module for example fails, a permanent error 
is usually assumed and no retry attempts are made. 

> Greetings,
> Rafael
>
>
> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> ---
>  kernel/kmod.c |   76
> ++++++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed,
> 66 insertions(+), 10 deletions(-)
>
> Index: linux-2.6.22-rc4-mm2/kernel/kmod.c
> ===================================================================
> --- linux-2.6.22-rc4-mm2.orig/kernel/kmod.c
> +++ linux-2.6.22-rc4-mm2/kernel/kmod.c
> @@ -41,14 +41,6 @@ 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
>
>  /*
> @@ -275,6 +267,30 @@ static void __call_usermodehelper(struct
>  	}
>  }
>
> +#ifdef CONFIG_PM
> +/*
> + * If set and if call_usermodehelper_exec() is supposed to wait, it will
> 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;
> +
> +/* Number of helpers running */
> +static atomic_t running_helpers = ATOMIC_INIT(0);
> +
> +/*
> + * Wait queue head used by usermodehelper_pm_callback() to wait for all
> running + * helpers to finish.
> + */
> +static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
> +
> +/*
> + * Time to wait for running_helpers to become zero before the setting of
> + * usermodehelper_disabled in usermodehelper_pm_callback() fails
> + */
> +#define RUNNING_HELPERS_TIMEOUT	(5 * HZ)
> +
>  static int usermodehelper_pm_callback(struct notifier_block *nfb,
>  					unsigned long action,
>  					void *ignored)
> @@ -283,7 +299,15 @@ static int usermodehelper_pm_callback(st
>  	case PM_HIBERNATION_PREPARE:
>  	case PM_SUSPEND_PREPARE:
>  		usermodehelper_disabled = 1;
> -		return NOTIFY_OK;
> +		wait_event_timeout(running_helpers_waitq,
> +					atomic_read(&running_helpers) == 0,
> +					RUNNING_HELPERS_TIMEOUT);
> +		if (atomic_read(&running_helpers) == 0) {
> +			return NOTIFY_OK;
> +		} else {
> +			usermodehelper_disabled = 0;
> +			return NOTIFY_BAD;
> +		}
>  	case PM_POST_HIBERNATION:
>  	case PM_POST_SUSPEND:
>  		usermodehelper_disabled = 0;
> @@ -293,6 +317,36 @@ static int usermodehelper_pm_callback(st
>  	return NOTIFY_DONE;
>  }
>
> +static void new_helper(void)
> +{
> +	atomic_inc(&running_helpers);
> +}
> +
> +static void helper_finished(void)
> +{
> +	if (atomic_dec_and_test(&running_helpers))
> +		wake_up(&running_helpers_waitq);
> +}
> +
> +#else /* CONFIG_PM */
> +#define usermodehelper_disabled	0
> +
> +static inline int usermodehelper_pm_callback(struct notifier_block *nfb,
          ^^^^^^
This kind of implies, the compiler might optimize this function away. Further 
down you call "pm_notifier(usermodehelper_pm_callback, 0);", thereby passing 
a pointer to usermodehelper_pm_callback which can't be inlined nor optimized 
away. If instead you had an inline function 
register_usermodehelper_pm_callback which called pm_notifier if CONFIG_PM was 
defined and did nothing otherwise...

> +						unsigned long action,
> +						void *ignored)
> +{
> +	return 0;
> +}
> +
> +static inline void new_helper(void)
> +{
> +}
> +
> +static inline void helper_finished(void)
> +{
> +}
> +#endif /* CONFIG_PM */
> +
>  /**
>   * call_usermodehelper_setup - prepare to call a usermode helper
>   * @path - path to usermode executable
> @@ -397,12 +451,13 @@ int call_usermodehelper_exec(struct subp
>  	DECLARE_COMPLETION_ONSTACK(done);
>  	int retval;
>
> +	new_helper();
>  	if (sub_info->path[0] == '\0') {
>  		retval = 0;
>  		goto out;
>  	}
>
> -	if (!khelper_wq || usermodehelper_disabled) {
> +	if (!khelper_wq || (wait != UMH_NO_WAIT && usermodehelper_disabled)) {
>  		retval = -EBUSY;
>  		goto out;
>  	}
> @@ -418,6 +473,7 @@ int call_usermodehelper_exec(struct subp
>
>    out:
>  	call_usermodehelper_freeinfo(sub_info);
> +	helper_finished();
>  	return retval;
>  }
>  EXPORT_SYMBOL(call_usermodehelper_exec);


-- 

------- ROAD ...the handyPC Company - - -  ) ) )

Uli Luckas
Software Development

ROAD GmbH
Bennigsenstr. 14 | 12159 Berlin | Germany
fon: +49 (30) 230069 - 64 | fax: +49 (30) 230069 - 69
url: www.road.de

Amtsgericht Charlottenburg: HRB 96688 B
Managing directors: Hans-Peter Constien, Hubertus von Streit