Re: [RESEND PATCH v2] PCI: Fix incorrect unlocking in pci_slot_trylock()

[dan.j.williams]

Jinhui Guo wrote:
> 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 the commit, 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 the commit 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.
> 
> Fixes: a4e772898f8b ("PCI: Add missing bridge lock to pci_bus_lock()")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jinhui Guo <guojinhui.liam@xxxxxxxxxxxxx>
> ---
> 
> Hi, all
> 
> Resent v2 to drop the Acked-by tag; no code changes. Sorry for the noise again.
> 
> v1: https://lore.kernel.org/all/20251211123635.2215-1-guojinhui.liam@xxxxxxxxxxxxx/
> 
> Changelog in v1 -> v2
>  - The v1 commit message was too brief, so I’ve sent v2 with more detail.
>  - Remove the braces from the if (!pci_bus_trylock(dev->subordinate)) statement.
> 
> Best Regards,
> Jinhui

I ended up also reviewing Keith's version of the same [1], but since this
one was posted earlier, go with this one.

Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>

[1]: http://lore.kernel.org/20260116184150.3013258-1-kbusch@xxxxxxxx