PCI: Do not treat EPROBE_DEFER as device attach failure

l1k · bjorn-helgaas · commit 9a2a5a638f8e · 2016-05-02T13:49:11.000-05:00
Linux 4.5 introduced a behavioral change in device probing during the suspend process with commit 013c074 ("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 subsystems 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 ab1a187 ("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. Fixes: ab1a187 ("PCI: Check device_attach() return value always") Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Grygorii Strashko <grygorii.strashko@ti.com> Cc: Alan Stern <stern@rowland.harvard.edu>
diff --git 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);
