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Date: Thu, 6 Mar 2008 22:28:27 +0100
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Alan Stern <stern@...land.harvard.edu>
Cc: pm list <linux-pm@...ts.linux-foundation.org>,
Alexey Starikovskiy <astarikovskiy@...e.de>,
Pavel Machek <pavel@....cz>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM: Make PM core handle device registrations concurrent with suspend/hibernation
On Thursday, 6 of March 2008, Alan Stern wrote:
> On Thu, 6 Mar 2008, Rafael J. Wysocki wrote:
>
> > On Thursday, 6 of March 2008, Alan Stern wrote:
> > > On Thu, 6 Mar 2008, Rafael J. Wysocki wrote:
> > >
> > > > > I thought of one more thing you might want to add: device_pm_add()
> > > > > doesn't handle the case where dev->parent is NULL.
> > > >
> > > > I'm not sure what you mean.
> > > >
> > > > If dev->parent is NULL, we get into the "successful" branch where the device is
> > > > added to dpm_active. Do you think we should add any extra handling of this
> > > > case?
> > >
> > > If a device is registered after dpm_suspend() has returned, the
> > > device won't be suspended properly before the system goes to sleep.
> > >
> > > If the device has a parent then you're okay, because the parent must
> > > already be suspended and so device_pm_add() will fail. But if the
> > > device doesn't have a parent then device_pm_add() will succeed, which
> > > you don't want.
> >
> > Well, can it happen in practice? If it can, then what way can it happen?
>
> Yes, it can happen in practice when a new module is loaded. In some
> ways, modules' init routines are like probe methods.
Hmm, I'm not sure if it really is possible to load a module when all devices
have been suspended. Never mind, though.
> Maybe it can happen some other ways too, but I don't know of any.
>
> > It seems to me that we're discussing purely academic stuff here. If it turns
> > out to be of any practical relevance, it will be trivial to add the handling of
> > it in the future.
>
> To be safe, I think we should make system sleep mutually exclusive with
> module loading.
Okay, is the (yet another) version of the patch below fine by you?
Rafael
---
From: Rafael J. Wysocki <rjw@...k.pl>
Modify the PM core to protect its data structures, specifically the
dpm_active list, from being corrupted if a child of the currently
suspending device is registered concurrently with its ->suspend()
callback. In that case, since the new device (the child) is added
to dpm_active after its parent, the PM core will attempt to
suspend it after the parent, which is wrong.
Introduce a new member of struct dev_pm_info, called 'sleeping',
and use it to check if the parent of the device being added to
dpm_active has been suspended, in which case the device registration
fails. Also, use 'sleeping' for checking if the ordering of devices
on dpm_active is correct.
Remove pm_sleep_rwsem which is not necessary any more.
Special thanks to Alan Stern for discussions and suggestions that
lead to the creation of this patch.
Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
Documentation/power/devices.txt | 5 +++
drivers/base/core.c | 6 +++-
drivers/base/power/main.c | 57 ++++++++++++++++++----------------------
drivers/base/power/power.h | 23 ++--------------
include/linux/pm.h | 1
5 files changed, 40 insertions(+), 52 deletions(-)
Index: linux-2.6/include/linux/pm.h
===================================================================
--- linux-2.6.orig/include/linux/pm.h
+++ linux-2.6/include/linux/pm.h
@@ -183,6 +183,7 @@ typedef struct pm_message {
struct dev_pm_info {
pm_message_t power_state;
unsigned can_wakeup:1;
+ bool sleeping:1; /* Owned by the PM core */
#ifdef CONFIG_PM_SLEEP
unsigned should_wakeup:1;
struct list_head entry;
Index: linux-2.6/drivers/base/power/main.c
===================================================================
--- linux-2.6.orig/drivers/base/power/main.c
+++ linux-2.6/drivers/base/power/main.c
@@ -54,7 +54,8 @@ static LIST_HEAD(dpm_destroy);
static DEFINE_MUTEX(dpm_list_mtx);
-static DECLARE_RWSEM(pm_sleep_rwsem);
+/* 'true' if all devices have been suspended, protected by dpm_list_mtx */
+static bool all_sleeping;
int (*platform_enable_wakeup)(struct device *dev, int is_on);
@@ -62,14 +63,28 @@ int (*platform_enable_wakeup)(struct dev
* device_pm_add - add a device to the list of active devices
* @dev: Device to be added to the list
*/
-void device_pm_add(struct device *dev)
+int device_pm_add(struct device *dev)
{
+ int error = 0;
+
pr_debug("PM: Adding info for %s:%s\n",
dev->bus ? dev->bus->name : "No Bus",
kobject_name(&dev->kobj));
mutex_lock(&dpm_list_mtx);
- list_add_tail(&dev->power.entry, &dpm_active);
+ if ((dev->parent && dev->parent->power.sleeping) || all_sleeping) {
+ if (dev->parent->power.sleeping)
+ dev_warn(dev,
+ "parent %s is sleeping, will not add\n",
+ dev->parent->bus_id);
+ else
+ dev_warn(dev, "devices are sleeping, will not add\n");
+ WARN_ON(true);
+ error = -EBUSY;
+ } else {
+ list_add_tail(&dev->power.entry, &dpm_active);
+ }
mutex_unlock(&dpm_list_mtx);
+ return error;
}
/**
@@ -107,32 +122,6 @@ void device_pm_schedule_removal(struct d
}
EXPORT_SYMBOL_GPL(device_pm_schedule_removal);
-/**
- * pm_sleep_lock - mutual exclusion for registration and suspend
- *
- * Returns 0 if no suspend is underway and device registration
- * may proceed, otherwise -EBUSY.
- */
-int pm_sleep_lock(void)
-{
- if (down_read_trylock(&pm_sleep_rwsem))
- return 0;
-
- return -EBUSY;
-}
-
-/**
- * pm_sleep_unlock - mutual exclusion for registration and suspend
- *
- * This routine undoes the effect of device_pm_add_lock
- * when a device's registration is complete.
- */
-void pm_sleep_unlock(void)
-{
- up_read(&pm_sleep_rwsem);
-}
-
-
/*------------------------- Resume routines -------------------------*/
/**
@@ -242,11 +231,13 @@ static int resume_device(struct device *
static void dpm_resume(void)
{
mutex_lock(&dpm_list_mtx);
+ all_sleeping = false;
while(!list_empty(&dpm_off)) {
struct list_head *entry = dpm_off.next;
struct device *dev = to_device(entry);
list_move_tail(entry, &dpm_active);
+ dev->power.sleeping = false;
mutex_unlock(&dpm_list_mtx);
resume_device(dev);
mutex_lock(&dpm_list_mtx);
@@ -285,7 +276,6 @@ void device_resume(void)
might_sleep();
dpm_resume();
unregister_dropped_devices();
- up_write(&pm_sleep_rwsem);
}
EXPORT_SYMBOL_GPL(device_resume);
@@ -426,6 +416,9 @@ static int dpm_suspend(pm_message_t stat
struct list_head *entry = dpm_active.prev;
struct device *dev = to_device(entry);
+ WARN_ON(dev->parent && dev->parent->power.sleeping);
+
+ dev->power.sleeping = true;
mutex_unlock(&dpm_list_mtx);
error = suspend_device(dev, state);
mutex_lock(&dpm_list_mtx);
@@ -437,11 +430,14 @@ static int dpm_suspend(pm_message_t stat
(error == -EAGAIN ?
" (please convert to suspend_late)" :
""));
+ dev->power.sleeping = false;
break;
}
if (!list_empty(&dev->power.entry))
list_move(&dev->power.entry, &dpm_off);
}
+ if (!error)
+ all_sleeping = true;
mutex_unlock(&dpm_list_mtx);
return error;
@@ -459,7 +455,6 @@ int device_suspend(pm_message_t state)
int error;
might_sleep();
- down_write(&pm_sleep_rwsem);
error = dpm_suspend(state);
if (error)
device_resume();
Index: linux-2.6/drivers/base/power/power.h
===================================================================
--- linux-2.6.orig/drivers/base/power/power.h
+++ linux-2.6/drivers/base/power/power.h
@@ -11,30 +11,13 @@ static inline struct device *to_device(s
return container_of(entry, struct device, power.entry);
}
-extern void device_pm_add(struct device *);
+extern int device_pm_add(struct device *);
extern void device_pm_remove(struct device *);
-extern int pm_sleep_lock(void);
-extern void pm_sleep_unlock(void);
#else /* CONFIG_PM_SLEEP */
-
-static inline void device_pm_add(struct device *dev)
-{
-}
-
-static inline void device_pm_remove(struct device *dev)
-{
-}
-
-static inline int pm_sleep_lock(void)
-{
- return 0;
-}
-
-static inline void pm_sleep_unlock(void)
-{
-}
+static inline int device_pm_add(struct device *dev) { return 0; }
+static inline void device_pm_remove(struct device *dev) {}
#endif
Index: linux-2.6/drivers/base/core.c
===================================================================
--- linux-2.6.orig/drivers/base/core.c
+++ linux-2.6/drivers/base/core.c
@@ -815,7 +815,11 @@ int device_add(struct device *dev)
error = dpm_sysfs_add(dev);
if (error)
goto PMError;
- device_pm_add(dev);
+ error = device_pm_add(dev);
+ if (error) {
+ dpm_sysfs_remove(dev);
+ goto PMError;
+ }
error = bus_add_device(dev);
if (error)
goto BusError;
Index: linux-2.6/Documentation/power/devices.txt
===================================================================
--- linux-2.6.orig/Documentation/power/devices.txt
+++ linux-2.6/Documentation/power/devices.txt
@@ -196,6 +196,11 @@ its parent; and can't be removed or susp
The policy is that the device tree should match hardware bus topology.
(Or at least the control bus, for devices which use multiple busses.)
+In particular, this means that a device registration may fail if the parent of
+the device is suspending (ie. has been chosen by the PM core as the next
+device to suspend) or has already suspended, as well as after all of the other
+devices have been suspended. Device drivers must be prepared to cope with such
+situations.
Suspending Devices
--
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