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"): pci_bus_add_device() no
longer sets dev->is_added = 1 if device_attach() returned a negative
value. This results in a BUG lockup in pci_bus_add_devices().
Fix the latter by not recursing to a child bus if device_attach() failed
for the bridge leading to it.
Fix the former by not interpreting -EPROBE_DEFER as failure. The device
will be probed eventually 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.
Note that even postponing the code in pciehp_resume() until the
complete phase wouldn't avoid these troubles because dpm_complete()
calls device_unblock_probing() only after ->complete has been
executed for all devices. We lack a pm hook from which it would
be safe to check a hotplug port and call device_attach() without
risking -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>
---
drivers/pci/bus.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 6c9f546..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);
@@ -324,7 +324,9 @@ void pci_bus_add_devices(const struct pci_bus *bus)
}
list_for_each_entry(dev, &bus->devices, bus_list) {
- BUG_ON(!dev->is_added);
+ /* Skip if device attach failed */
+ if (!dev->is_added)
+ continue;
child = dev->subordinate;
if (child)
pci_bus_add_devices(child);
--
2.8.0.rc3
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