On Tue, Nov 9, 2021 at 7:59 AM Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> wrote: > > Hello, > > On Mon, Nov 08, 2021 at 08:56:19PM -0600, Bjorn Helgaas wrote: > > [+cc Greg: new device_is_bound() use] > > ack, that's what I would have suggested now, too. > > > On Mon, Nov 08, 2021 at 10:22:26PM +0100, Uwe Kleine-König wrote: > > > pci_pm_runtime_resume() exits early when the device to resume isn't > > > bound yet: > > > > > > if (!to_pci_driver(dev->driver)) > > > return 0; > > > > > > This however isn't true when the device currently probes and > > > local_pci_probe() calls pm_runtime_get_sync() because then the driver > > > core already setup dev->driver. As a result the driver's resume callback > > > is called before the driver's probe function is called and so more often > > > than not required driver data isn't setup yet. > > > > > > So replace the check for the device being unbound by a check that only > > > becomes true after .probe() succeeded. > > > > I like the fact that this patch is short and simple. > > > > But there are 30+ users of to_pci_driver(). This patch asserts that > > *one* of them, pci_pm_runtime_resume(), is special and needs to test > > device_is_bound() instead of using to_pci_driver(). > > Maybe for the other locations using device_is_bound(&pdev->dev) instead > of to_pci_driver(pdev) != NULL would be nice, too? > > I have another doubt: device_is_bound() should (according to its > kernel-doc) be called with the device lock held. For the call stack that > is (maybe) fixed here, the lock is held (by __device_attach). We > probably should check if the lock is also held for the other calls of > pci_pm_runtime_resume(). > > Hmm, the device lock is a mutex, the pm functions might be called in > atomic context, right? > > > It's special because the current PM implementation calls it via > > pm_runtime_get_sync() before the driver's .probe() method. That > > connection is a little bit obscure and fragile. What if the PM > > implementation changes? > > Maybe a saver bet would be to not use pm_runtime_get_sync() in > local_pci_probe()? Yes, in principle it might be replaced with pm_runtime_get_noresume(). In theory, that may be problematic if a device is put into a low-power state on remove and then the driver is bound again to it. > I wonder if the same problem exists on remove, i.e. pci_device_remove() > calls pm_runtime_put_sync() after the driver's .remove() callback was > called. If it is called after ->remove() and before clearing the device's driver pointer, then yes. If this is turned into pm_runtime_put_noidle(), all should work. > > Maybe we just need a comment there about why it looks different than > > the other PM interfaces? > > A comment is a good idea for sure.
