PCI/pwrctrl: Cancel outstanding rescan work when unregistering

It's possible to trigger use-after-free here by:

  (a) forcing rescan_work_func() to take a long time and
  (b) utilizing a pwrctrl driver that may be unloaded for some reason

Cancel outstanding work to ensure it is finished before we allow our data
structures to be cleaned up.

[bhelgaas: tidy commit log]
Fixes: 8f62819 ("PCI/pwrctl: Rescan bus on a separate thread")
Signed-off-by: Brian Norris <[email protected]>
Signed-off-by: Brian Norris <[email protected]>
Signed-off-by: Krzysztof Wilczyński <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Manivannan Sadhasivam <[email protected]>
Acked-by: Bartosz Golaszewski <[email protected]>
Cc: Konrad Dybcio <[email protected]>
Link: https://patch.msgid.link/20250409115313.1.Ia319526ed4ef06bec3180378c9a008340cec9658@changeid

Author: computersforpeace

drivers/pci/pwrctrl/core.c

@@ -101,6 +101,8 @@ EXPORT_SYMBOL_GPL(pci_pwrctrl_device_set_ready);
  */
 void pci_pwrctrl_device_unset_ready(struct pci_pwrctrl *pwrctrl)
 {
+	cancel_work_sync(&pwrctrl->work);
+
 	/*
 	 * We don't have to delete the link here. Typically, this function
 	 * is only called when the power control device is being detached. If