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SubjectRe: [RFC][PATCH] PM: Make PM core handle device registrations concurrent with suspend/hibernation
Date
On Wednesday, 5 of March 2008, Alan Stern wrote:
> On Wed, 5 Mar 2008, Rafael J. Wysocki wrote:
>
> > -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) {
> > + WARN_ON(true);
>
> I would prefer to put a dev_warn() line here, so that people reading
> the kernel log can easily tell which device caused the problem and what
> sort of problem it is. Something like this:
>
> dev_warn(dev, "device added while parent %s is asleep\n",
> dev->parent->bus_id);
> WARN_ON(true);

Added.

> > @@ -426,6 +406,12 @@ static int dpm_suspend(pm_message_t stat
> > struct list_head *entry = dpm_active.prev;
> > struct device *dev = to_device(entry);
> >
> > + if (dev->parent && dev->parent->power.sleeping) {
> > + WARN_ON(true);
> > + error = -EAGAIN;
> > + break;
>
> Again, a dev_warn() would be appropriate.

I chose just "WARN_ON(dev->parent && dev->parent->power.sleeping)",
which is shorter. :-)

I don't really expect it to appear and if it's reported, it'll be easy to
figure out everything from the stack trace.

Revised patch below.

Thanks,
Rafael

---
From: Rafael J. Wysocki <rjw@sisk.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@sisk.pl>
---
Documentation/power/devices.txt | 4 +++
drivers/base/core.c | 6 ++++
drivers/base/power/main.c | 50 ++++++++++++++--------------------------
drivers/base/power/power.h | 23 ++----------------
include/linux/pm.h | 1
5 files changed, 31 insertions(+), 53 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
@@ -54,22 +54,31 @@ static LIST_HEAD(dpm_destroy);

static DEFINE_MUTEX(dpm_list_mtx);

-static DECLARE_RWSEM(pm_sleep_rwsem);
-
int (*platform_enable_wakeup)(struct device *dev, int is_on);

/**
* 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) {
+ dev_warn(dev,
+ "refusing to add device while parent %s is asleep\n",
+ dev->parent->bus_id);
+ WARN_ON(true);
+ error = -EBUSY;
+ } else {
+ list_add_tail(&dev->power.entry, &dpm_active);
+ }
mutex_unlock(&dpm_list_mtx);
+ return error;
}

/**
@@ -107,32 +116,6 @@ 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 -------------------------*/

/**
@@ -247,6 +230,7 @@ static void dpm_resume(void)
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 +269,6 @@ void device_resume(void)
might_sleep();
dpm_resume();
unregister_dropped_devices();
- up_write(&pm_sleep_rwsem);
}
EXPORT_SYMBOL_GPL(device_resume);

@@ -426,6 +409,9 @@ 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);
@@ -437,6 +423,7 @@ 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))
@@ -459,7 +446,6 @@ 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 +196,10 @@ 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. Device drivers must be prepared
+to cope with such situations.


Suspending Devices

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