[PATCH AUTOSEL 5.4 6/7] PCI: Add missing bridge lock to pci_bus_lock()

Sasha Levin
2024-07-28T16:10:49Z

From: Dan Williams <dan.j.williams@intel.com>

[ Upstream commit a4e772898f8bf2e7e1cf661a12c60a5612c4afab ]

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().

Link: https://lore.kernel.org/r/171711747501.1628941.15217746952476635316.stgit@dwillia2-xfh.jf.intel.com
Reported-by: Imre Deak <imre.deak@intel.com>
Closes: http://lore.kernel.org/r/6657833b3b5ae_14984b29437@dwillia2-xfh.jf.intel.com.notmuch
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
[bhelgaas: squash in recursive locking deadlock fix from Keith Busch:
https://lore.kernel.org/r/20240711193650.701834-1-kbusch@meta.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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/pci/pci.c | 35 +++++++++++++++++++++--------------
1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index deafd229ef8b4..41050a35631fa 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5200,10 +5200,12 @@ 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)
pci_bus_lock(dev->subordinate);
+ else
+ pci_dev_lock(dev);
}
}

@@ -5215,8 +5217,10 @@ static void pci_bus_unlock(struct pci_bus *bus)
list_for_each_entry(dev, &bus->devices, bus_list) {
if (dev->subordinate)
pci_bus_unlock(dev->subordinate);
- pci_dev_unlock(dev);
+ else
+ pci_dev_unlock(dev);
}
+ pci_dev_unlock(bus->self);
}

/* Return 1 on successful lock, 0 on contention */
@@ -5224,15 +5228,15 @@ static int pci_bus_trylock(struct pci_bus *bus)
{
struct pci_dev *dev;

+ if (!pci_dev_trylock(bus->self))
+ return 0;
+
list_for_each_entry(dev, &bus->devices, bus_list) {
- if (!pci_dev_trylock(dev))
- goto unlock;
if (dev->subordinate) {
- if (!pci_bus_trylock(dev->subordinate)) {
- pci_dev_unlock(dev);
+ if (!pci_bus_trylock(dev->subordinate))
goto unlock;
- }
- }
+ } else if (!pci_dev_trylock(dev))
+ goto unlock;
}
return 1;

@@ -5240,8 +5244,10 @@ static int pci_bus_trylock(struct pci_bus *bus)
list_for_each_entry_continue_reverse(dev, &bus->devices, bus_list) {
if (dev->subordinate)
pci_bus_unlock(dev->subordinate);
- pci_dev_unlock(dev);
+ else
+ pci_dev_unlock(dev);
}
+ pci_dev_unlock(bus->self);
return 0;
}

@@ -5273,9 +5279,10 @@ static void pci_slot_lock(struct pci_slot *slot)
list_for_each_entry(dev, &slot->bus->devices, bus_list) {
if (!dev->slot || dev->slot != slot)
continue;
- pci_dev_lock(dev);
if (dev->subordinate)
pci_bus_lock(dev->subordinate);
+ else
+ pci_dev_lock(dev);
}
}

@@ -5301,14 +5308,13 @@ static int pci_slot_trylock(struct pci_slot *slot)
list_for_each_entry(dev, &slot->bus->devices, bus_list) {
if (!dev->slot || dev->slot != slot)
continue;
- if (!pci_dev_trylock(dev))
- goto unlock;
if (dev->subordinate) {
if (!pci_bus_trylock(dev->subordinate)) {
pci_dev_unlock(dev);
goto unlock;
}
- }
+ } else if (!pci_dev_trylock(dev))
+ goto unlock;
}
return 1;

@@ -5319,7 +5325,8 @@ static int pci_slot_trylock(struct pci_slot *slot)
continue;
if (dev->subordinate)
pci_bus_unlock(dev->subordinate);
- pci_dev_unlock(dev);
+ else
+ pci_dev_unlock(dev);
}
return 0;
}
--
2.43.0