On Mon, 7 Jan 2008, Rafael J. Wysocki wrote: > 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?). 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? I was thinking that it might be called before lock_all_devices(). However let's ignore that possibility and simplify the discussion by assuming that destroy_suspended_device() is never called except by a suspend or resume method for that device or one of its ancestors. (This still leaves the possibility that it might get called by mistake during a runtime suspend or resume...) > > 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. The same problem affects the synchronous approach. We can fix it by having dpm_suspend() do the list_move() before calling suspend_device(). Then if the suspend fails move the device back. > One more question: is there any particular reason not to call > device_pm_remove() at the beginning of device_del()? I think it's done this way to avoid having a window where the device isn't on a PM list and is still owned by the bus and the driver. But if a suspend occurs during that window, it shouldn't matter that the device will be left unsuspended. After all, the same thing would have happened if the suspend occurred after bus_remove_device(). So no, there shouldn't be a problem with moving the call. Alan Stern - 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
