On Monday, 7 of January 2008, Alan Stern wrote: > On Mon, 7 Jan 2008, Rafael J. Wysocki wrote: > > > Please see the patch at: http://lkml.org/lkml/2008/1/6/298 . It represents my > > current idea about how to do that. > > It has some problems. > > First, note that the list manipulations in dpm_suspend(), > device_power_down(), and so on aren't protected by dpm_list_mtx. So > your patch could corrupt the list pointers. Yes, they need the locking. I have overlooked that, mostly because the locking was removed by gregkh-driver-pm-acquire-device-locks-prior-to-suspending.patch too (because you assumed there woundn't be any need to remove a device during a suspend, right?). > Are you assuming that no other threads can be running at this time? No, I'm not. > Note also that device_pm_destroy_suspended() does up(&dev->sem), but it > doesn't know whether or not dev->sem was locked to begin with. Do you mean it might have been released already by another thread calling device_pm_destroy_suspended() on the same device? > Do you want to rule out the possibility of a driver's suspend or remove > methods calling destroy_suspended_device() on its own device? With > your synchronous approach, this would mean that the suspend/resume > method would indirectly end up calling the remove method. This is > dangerous at best; with USB it would be a lockdep violation. With an > asynchronous approach, on the other hand, this wouldn't be a problem. Well, the asynchronous apprach has the problem that the device may end up on a wrong list when removed by one of the .suspend() callbacks (and I don't see how to avoid that without extra complexity). Perhaps that's something we can live with, though. One more question: is there any particular reason not to call device_pm_remove() at the beginning of device_del()? Rafael - To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
