[PATCH v2] PCI: take the rescan lock when adding devices during host probe

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

Since adding the PCI power control code, we may end up with a race
between the pwrctl platform device rescanning the bus and the host
controller probe function. The latter needs to take the rescan lock when
adding devices or we may end up in an undefined state having two
incompletely added devices and hit the following crash when trying to
remove the device over sysfs:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Internal error: Oops: 0000000096000004 [#1] SMP
Call trace:
  __pi_strlen+0x14/0x150
  kernfs_find_ns+0x80/0x13c
  kernfs_remove_by_name_ns+0x54/0xf0
  sysfs_remove_bin_file+0x24/0x34
  pci_remove_resource_files+0x3c/0x84
  pci_remove_sysfs_dev_files+0x28/0x38
  pci_stop_bus_device+0x8c/0xd8
  pci_stop_bus_device+0x40/0xd8
  pci_stop_and_remove_bus_device_locked+0x28/0x48
  remove_store+0x70/0xb0
  dev_attr_store+0x20/0x38
  sysfs_kf_write+0x58/0x78
  kernfs_fop_write_iter+0xe8/0x184
  vfs_write+0x2dc/0x308
  ksys_write+0x7c/0xec

Reported-by: Konrad Dybcio <konradybcio@xxxxxxxxxx>
Tested-by: Konrad Dybcio <konradybcio@xxxxxxxxxx>
Fixes: 4565d2652a37 ("PCI/pwrctl: Add PCI power control core code")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
---
v1 -> v2:
- improve the commit message, add example stack trace

 drivers/pci/probe.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 4f68414c3086..f1615805f5b0 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -3105,7 +3105,9 @@ int pci_host_probe(struct pci_host_bridge *bridge)
 	list_for_each_entry(child, &bus->children, node)
 		pcie_bus_configure_settings(child);
 
+	pci_lock_rescan_remove();
 	pci_bus_add_devices(bus);
+	pci_unlock_rescan_remove();
 	return 0;
 }
 EXPORT_SYMBOL_GPL(pci_host_probe);
-- 
2.30.2