PCI: Fix pci_slot_trylock() error handling

[ 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@meta.com]

Fixes: a4e772898f8b ("PCI: Add missing bridge lock to pci_bus_lock()")
Signed-off-by: Jinhui Guo <guojinhui.liam@bytedance.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251212145528.2555-1-guojinhui.liam@bytedance.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 7858121344655049c20a232afe4dfa28909876f8..d4e70570d09f2f75a146264dd53b6be34c740364 100644 (file)
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5500,10 +5500,8 @@ 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;
        }