On Wednesday, 20 of February 2008, Alan Stern wrote:
> On Wed, 20 Feb 2008, Rafael J. Wysocki wrote:
>
> > Well, below is an uncompiled and untested but illustrating the idea that
> > might allow people not to bother with device_pm_schedule_removal()
> > explicitly and can fix the issue at hand.
> >
> > [There are some cases that need handling and are not covered here.]
> >
> > Please have a look.
> >
> > Thanks,
> > Rafael
>
> > +static struct task_struct *suspending_task;
> > +static DEFINE_MUTEX(suspending_task_mtx);
>
> I suspect you don't really need this mutex.
>
> > +bool in_suspend_context(void)
> > +{
> > + bool result;
> > +
> > + mutex_lock(&suspending_task_mtx);
> > + result = (suspending_task == current);
> > + mutex_unlock(&suspending_task_mtx);
> > + return result;
> > +}
>
> If suspending_task == current then you are guaranteed to be serialized,
> because everything a single task does is serial.
As I said before (but that doesn't seem to reach the list, so I'm repeating),
this is to protect other tasks from reading an inconsistent value of
suspending_task in case they attempt to remove a device concurrently with
respect to us.
While this is not likely to happen right now, because of the freezer, it may
very well happen when the freezer is finally removed.
> > @@ -1162,7 +1162,10 @@ void device_destroy(struct class *class,
> > dev = class_find_device(class, &devt, __match_devt);
> > if (dev) {
> > put_device(dev);
> > - device_unregister(dev);
> > + if (in_suspend_context())
> > + device_pm_schedule_removal(dev);
> > + else
> > + device_unregister(dev);
> > }
> > }
>
> But what about device_del()? Can a similar change be made there?
Something like the patch below, perhaps? Again, untested, but compiled this
time. :-)
Thanks,
Rafael
---
drivers/base/core.c | 5 +++++
drivers/base/power/main.c | 22 ++++++++++++++++++++++
drivers/base/power/power.h | 5 +++++
3 files changed, 32 insertions(+)
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
@@ -59,6 +59,26 @@ static DECLARE_RWSEM(pm_sleep_rwsem);
int (*platform_enable_wakeup)(struct device *dev, int is_on);
+static struct task_struct *suspending_task;
+static DEFINE_MUTEX(suspending_task_mtx);
+
+bool in_suspend_context(void)
+{
+ bool result;
+
+ mutex_lock(&suspending_task_mtx);
+ result = (suspending_task == current);
+ mutex_unlock(&suspending_task_mtx);
+ return result;
+}
+
+static void set_suspending_task(struct task_struct *task)
+{
+ mutex_lock(&suspending_task_mtx);
+ suspending_task = task;
+ mutex_unlock(&suspending_task_mtx);
+}
+
/**
* device_pm_add - add a device to the list of active devices
* @dev: Device to be added to the list
@@ -272,6 +292,7 @@ static void dpm_resume(void)
mutex_lock(&dpm_list_mtx);
}
mutex_unlock(&dpm_list_mtx);
+ set_suspending_task(NULL);
}
/**
@@ -460,6 +481,7 @@ static int dpm_suspend(pm_message_t stat
{
int error = 0;
+ set_suspending_task(current);
mutex_lock(&dpm_list_mtx);
while (!list_empty(&dpm_locked)) {
struct list_head *entry = dpm_locked.prev;
Index: linux-2.6/drivers/base/core.c
===================================================================
--- linux-2.6.orig/drivers/base/core.c
+++ linux-2.6/drivers/base/core.c
@@ -929,6 +929,11 @@ void device_del(struct device *dev)
struct device *parent = dev->parent;
struct class_interface *class_intf;
+ if (in_suspend_context()) {
+ get_device(dev);
+ device_pm_schedule_removal(dev);
+ return;
+ }
device_pm_remove(dev);
if (parent)
klist_del(&dev->knode_parent);
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
@@ -11,6 +11,7 @@ static inline struct device *to_device(s
return container_of(entry, struct device, power.entry);
}
+extern bool in_suspend_context(void);
extern void device_pm_add(struct device *);
extern void device_pm_remove(struct device *);
extern int pm_sleep_lock(void);
@@ -18,6 +19,10 @@ extern void pm_sleep_unlock(void);
#else /* CONFIG_PM_SLEEP */
+static inline bool in_suspend_context(void)
+{
+ return false;
+}
static inline void device_pm_add(struct device *dev)
{
--
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