On Sunday, 6 of January 2008, Alan Stern wrote: > On Sun, 6 Jan 2008, Rafael J. Wysocki wrote: > > > > Still, shouldn't we fail the removal of the device apart from giving the > > > warning? > > > > Actually, having thought about it a bit more, I don't see the point in > > preventing the removal of the device from the list in device_pm_remove() if > > we allow all of the operations in device_del() preceding it to be performed. > > That's not the issue. We _don't_ allow all of the operations in > device_del() preceding the call to device_pm_remove(). In particular, > the call to the device's driver's remove method will deadlock because > device_release_driver() always has to acquire dev->sem. > > > Shouldn't we just take pm_sleep_rwsem in device_del() upfront and block on > > that > > if locked? > > No -- the whole idea here is to print an error message in the system > log if a driver's resume method tries to call device_del(). Deadlock > is unavoidable in this case, but at least we'll know which driver is > guilty.
Still, if we do that, we won't need to acquire dev->sem in device_pm_remove() any more. Apart from this, by acqiring pm_sleep_rwsem for reading in device_del() we can prevent a suspend from starting while the device is being removed. Consider, for example, the scenario possible with the $subject patch: - device_del() starts and notices pm_sleep_rwsem unlocked, so the warning is not printed - it proceeds and everything before device_pm_remove() succeeds - now, device_suspend() is called and locks dev->sem - device_del() calls device_pm_remove() and blocks on that with the device partialy removed I think we should prevent this from happening. Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
