On Wednesday, April 20, 2016 04:44:27 PM Lukas Wunner wrote:
> Linux 4.5 introduced a behavioral change in device probing during the
> suspend process with commit 013c074f8642 ("PM / sleep: prohibit devices
> probing during suspend/hibernation"): It defers device probing during
> the entire suspend process, starting from the prepare phase and ending
> with the complete phase. A rule existed before that "we rely on sub-
> systems not to do any probing once a device is suspended" but it is
> enforced only now (Alan Stern, https://lkml.org/lkml/2015/9/15/908).
>
> This resulted in a WARN splat if a PCI device (e.g. Thunderbolt) is
> plugged in while the system is asleep: Upon waking up, pciehp_resume()
> discovers new devices in the resume phase and immediately tries to bind
> them to a driver. Since probing is now deferred, device_attach() returns
> -EPROBE_DEFER, which provoked a WARN in pci_bus_add_device().
>
> Linux 4.6-rc1 aggravates the situation with commit ab1a187bba5c ("PCI:
> Check device_attach() return value always"): If device_attach() returns
> a negative value, pci_bus_add_device() now removes the sysfs and procfs
> entries for the device and pci_bus_add_devices() subsequently locks up
> with a BUG. Even with the BUG fixed we're still in trouble because the
> device remains on the deferred probing list even though its sysfs and
> procfs entries are gone and its children won't be added.
>
> Fix by not interpreting -EPROBE_DEFER as failure. The device will be
> probed eventually (through device_unblock_probing() in dpm_complete())
> and there is proper locking in place to avoid races (e.g. if devices are
> unplugged again und thus deleted from the system before deferred probing
> happens, I have tested this). Also, those functions which dereference
> dev->driver (e.g. pci_pm_*()) do contain proper NULL pointer checks.
> So it seems safe to ignore -EPROBE_DEFER.
>
> Cc: Grygorii Strashko <grygorii.strashko@xxxxxx>
> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> Cc: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> v2: Split commit in two, explain when exactly deferred probing will
> happen (Bjorn Helgaas).
>
> drivers/pci/bus.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 23a39fd..dd7cdbe 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -294,7 +294,7 @@ void pci_bus_add_device(struct pci_dev *dev)
>
> dev->match_driver = true;
> retval = device_attach(&dev->dev);
> - if (retval < 0) {
> + if (retval < 0 && retval != -EPROBE_DEFER) {
> dev_warn(&dev->dev, "device attach failed (%d)\n", retval);
> pci_proc_detach_device(dev);
> pci_remove_sysfs_dev_files(dev);
>
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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