[PATCH 6.19 756/844] PCI: Fix pci_slot_trylock() error handling

[Sasha Levin]

From: Jinhui Guo <guojinhui.liam@xxxxxxxxxxxxx>

[ Upstream commit 9368d1ee62829b08aa31836b3ca003803caf0b72 ]

Commit a4e772898f8b ("PCI: Add missing bridge lock to pci_bus_lock()")
delegates the bridge device's pci_dev_trylock() to pci_bus_trylock() in
pci_slot_trylock(), but it forgets to remove the corresponding
pci_dev_unlock() when pci_bus_trylock() fails.

Before a4e772898f8b, the code did:

  if (!pci_dev_trylock(dev)) /* <- lock bridge device */
    goto unlock;
  if (dev->subordinate) {
    if (!pci_bus_trylock(dev->subordinate)) {
      pci_dev_unlock(dev);   /* <- unlock bridge device */
      goto unlock;
    }
  }

After a4e772898f8b the bridge-device lock is no longer taken, but the
pci_dev_unlock(dev) on the failure path was left in place, leading to the
bug.

This yields one of two errors:

  1. A warning that the lock is being unlocked when no one holds it.
  2. An incorrect unlock of a lock that belongs to another thread.

Fix it by removing the now-redundant pci_dev_unlock(dev) on the failure
path.

[Same patch later posted by Keith at
https://patch.msgid.link/20260116184150.3013258-1-kbusch@xxxxxxxx]

Fixes: a4e772898f8b ("PCI: Add missing bridge lock to pci_bus_lock()")
Signed-off-by: Jinhui Guo <guojinhui.liam@xxxxxxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://patch.msgid.link/20251212145528.2555-1-guojinhui.liam@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/pci/pci.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index a4eb3bc2127ae..8500b862f4f2e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5355,10 +5355,8 @@ static int pci_slot_trylock(struct pci_slot *slot)
 		if (!dev->slot || dev->slot != slot)
 			continue;
 		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;
 	}
-- 
2.51.0