Re: [patch]a lockless method to alter pm count

Am Donnerstag, 26. April 2007 16:40 schrieb Alan Stern:
> > > Either way is awkward, but mine is a little cleaner.  What do you think?
> > 
> > If you want me to think I can do that. If both solutions we come up
> > are awkward, we are doing something wrong. It seems to me we should
> > reduce the number of locks, not add new locks. Can we get rid of the
> > special pm lock, use a general lock and export that to the drivers?
> 
> No, that's impossible.  It's because the locking rules for the pm_mutex
> are opposite those for dev->sem: The order of acquisition of the dev->sem
> locks is _down_ the device tree, but the order of acquisition of the
> udev->pm_mutex locks is _up_ the device tree.
> 
> However in this particular case we may indeed be able to simplify things.  
> Just do this:
> 
> usb_stor_control_thread():
> usb_autopm_get_interface();
> mutex_lock(&us->dev_mutex);
> if (test_bit(US_FLIDX_DISCONNECTING, &us->flags)) ...
> 
> The only possible problem here is that the code does PM-related stuff at a
> time when we aren't certain the driver is still bound to the interface.  
> So change the way storage_disconnect() works; make it wait until the
> control thread has exited.  If we convert over to using kthread_stop()
> this will happen naturally.
> 
> I'll work on a patch to do that conversion...

OK, I see. I'll use the method you've proposed.

	Regards
		Oliver

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