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

Alan Stern
2008-02-21T16:28:32Z

On Thu, 21 Feb 2008, Rafael J. Wysocki wrote:

> > > +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.

Sorry, I don't understand. Are you worried that process A might set
suspending_task = A but then process B might still see suspending_task
== NULL? Or that A might set suspend_task = NULL but then B might
still see suspending_task == A?

Neither one will cause any problem, since the only case that matters is
when B sees suspending_task == B -- and that can happen if and only if
B was the last process to set suspending_task.

In fact, you might as well get rid of the set_suspending_task() routine
entirely and just put the assignments inline.

> --- 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()?

> + 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.

Alan Stern