PCI: Warn on missing cfg_access_lock during secondary bus reset

The recent adventure with adding lockdep tracking for cfg_access_lock,
while it yielded many false positives [1], did catch a true positive in the
pci_reset_bus() path [2].

So, while lockdep is difficult to deploy, open coding a check that
cfg_access_lock is held during the reset is feasible.

While this does not offer a full backtrace, it should be sufficient to
implicate the caller of pci_bridge_secondary_bus_reset() as a path that
needs investigation.

Link: https://lore.kernel.org/r/171711746953.1628941.4692125082286867825.stgit@dwillia2-xfh.jf.intel.com
Link: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_134186v1/shard-dg2-1/igt@device_reset@unbind-reset-rebind.html
Link: http://lore.kernel.org/r/cfb50601-5d2a-4676-a958-1bd3f1b06654@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Kalle Valo <kvalo@kernel.org>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 59e0949fb079d5f62edb5f93bd19a22f8b8d3d48..4821c22eca1fcd2dac6f89b34ea6bb962f108e12 100644 (file)
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4884,6 +4884,9 @@ void __weak pcibios_reset_secondary_bus(struct pci_dev *dev)
 int pci_bridge_secondary_bus_reset(struct pci_dev *dev)
 {
        lock_map_assert_held(&dev->cfg_access_lock);
+       if (!dev->block_cfg_access)
+               pci_warn_once(dev, "unlocked secondary bus reset via: %pS\n",
+                             __builtin_return_address(0));
        pcibios_reset_secondary_bus(dev);
 
        return pci_bridge_wait_for_secondary_bus(dev, "bus reset");