Re: [Bug 10030] Suspend doesn't work when SD card is inserted

Rafael J. Wysocki
2008-02-21T22:49:23Z

On Thursday, 21 of February 2008, Alan Stern wrote:
> On Thu, 21 Feb 2008, Rafael J. Wysocki wrote:
>
> > > > --- 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);
> > >
> > > Where is this get_device() undone? Shouldn't there be an extra
> > > put_device() added to unregister_dropped_devices()?
> >
> > No, I don't think so, because unregister_dropped_devices() calls
> > device_unregister() that does the put_device() eventually.
>
> Ah, yes.
>
> > If we are called by device_unregister(), the get_device() is needed to balance
> > the put_device() that will be called by device_unregister() after we return.
> >
> > OTOH, if we are called directly, then we need to balance the put_device()
> > that will be done by device_unregister() called from
> > unregister_dropped_devices().
> >
> > I hope I didn't miss anything.
>
> Okay, that sounds right.
>
> > > > + device_pm_schedule_removal(dev);
> > > > + return;
> > > > + }
> > > > device_pm_remove(dev);
> > > > if (parent)
> > > > klist_del(&dev->knode_parent);
> > >
> > > And now the change to device_destroy() isn't needed at all.
> >
> > No, it's not. Didn't I remove it? I thought I did.
>
> Oh yes, you did.
>
> I see a possible problem in device_resume(). My copy isn't fully
> up-to-date, but it looks like you call unregister_dropped_devices()
> before doing the up_write(&pm_sleep_rwsem). Won't this cause
> warnings in device_del() about a suspicious caller?

No, it won't, because the devices' semaphores are unlocked by
unregister_dropped_devices() before calling device_unregister().

BTW, below is a simplified version of the patch, without the mutex protecting
suspending_task. I'd like to push it upstream if it looks good.

Please also have a look at http://bugzilla.kernel.org/show_bug.cgi?id=10030.
There seems to be another issue related to us holding devices' semaphores.
Namely, it looks like, when the user removes the card, a concurrent thread
(from a workqueue) calls device_del() and blocks on the dev->sem held by
us and then something else deadlocks with this thread. I'll be looking into
this tomorrow.

Thanks,
Rafael

---
drivers/base/core.c | 5 +++++
drivers/base/power/main.c | 9 +++++++++
drivers/base/power/power.h | 5 +++++
3 files changed, 19 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 +59,13 @@ static DECLARE_RWSEM(pm_sleep_rwsem);

int (*platform_enable_wakeup)(struct device *dev, int is_on);

+static struct task_struct *suspending_task;
+
+bool in_suspend_context(void)
+{
+ return (suspending_task == current);
+}
+
/**
* device_pm_add - add a device to the list of active devices
* @dev: Device to be added to the list
@@ -272,6 +279,7 @@ static void dpm_resume(void)
mutex_lock(&dpm_list_mtx);
}
mutex_unlock(&dpm_list_mtx);
+ suspending_task = NULL;
}

/**
@@ -460,6 +468,7 @@ static int dpm_suspend(pm_message_t stat
{
int error = 0;

+ 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)
{