[PATCH v2 3/3] PCI: Add missing bridge lock to pci_bus_lock()

[Dan Williams <dan.j.williams@xxxxxxxxx>]

One of the true positives that the cfg_access_lock lockdep effort
identified is this sequence:

 WARNING: CPU: 14 PID: 1 at drivers/pci/pci.c:4886 pci_bridge_secondary_bus_reset+0x5d/0x70
 RIP: 0010:pci_bridge_secondary_bus_reset+0x5d/0x70
 Call Trace:
  <TASK>
  ? __warn+0x8c/0x190
  ? pci_bridge_secondary_bus_reset+0x5d/0x70
  ? report_bug+0x1f8/0x200
  ? handle_bug+0x3c/0x70
  ? exc_invalid_op+0x18/0x70
  ? asm_exc_invalid_op+0x1a/0x20
  ? pci_bridge_secondary_bus_reset+0x5d/0x70
  pci_reset_bus+0x1d8/0x270
  vmd_probe+0x778/0xa10
  pci_device_probe+0x95/0x120

Where pci_reset_bus() users are triggering unlocked secondary bus
resets. Ironically pci_bus_reset(), several calls down from
pci_reset_bus(), uses pci_bus_lock() before issuing the reset which
locks everything *but* the bridge itself.

For the same motivation as adding:

    bridge = pci_upstream_bridge(dev);
    if (bridge)
            pci_dev_lock(bridge);

...to pci_reset_function() for the "bus" and "cxl_bus" reset cases, add
pci_dev_lock() for @bus->self to pci_bus_lock().

Reported-by: Imre Deak <imre.deak@xxxxxxxxx>
Closes: http://lore.kernel.org/r/6657833b3b5ae_14984b29437@xxxxxxxxxxxxxxxxxxxxxxxxx.notmuch
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 drivers/pci/pci.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8df32a3a0979..aac5daad3188 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5444,6 +5444,7 @@ static void pci_bus_lock(struct pci_bus *bus)
 {
 	struct pci_dev *dev;
 
+	pci_dev_lock(bus->self);
 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		pci_dev_lock(dev);
 		if (dev->subordinate)
@@ -5461,6 +5462,7 @@ static void pci_bus_unlock(struct pci_bus *bus)
 			pci_bus_unlock(dev->subordinate);
 		pci_dev_unlock(dev);
 	}
+	pci_dev_unlock(bus->self);
 }
 
 /* Return 1 on successful lock, 0 on contention */
@@ -5468,6 +5470,7 @@ static int pci_bus_trylock(struct pci_bus *bus)
 {
 	struct pci_dev *dev;
 
+	pci_dev_lock(bus->self);
 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		if (!pci_dev_trylock(dev))
 			goto unlock;
@@ -5486,6 +5489,7 @@ static int pci_bus_trylock(struct pci_bus *bus)
 			pci_bus_unlock(dev->subordinate);
 		pci_dev_unlock(dev);
 	}
+	pci_dev_unlock(bus->self);
 	return 0;
 }