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>
---
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);
--
2.8.0.rc3
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