PCI: endpoint: Clear secondary (not primary) EPC in pci_epc_remove_epf()

In addition to a primary endpoint controller, an endpoint function may be
associated with a secondary endpoint controller, epf->sec_epc, to provide
NTB (non-transparent bridge) functionality.

Previously, pci_epc_remove_epf() incorrectly cleared epf->epc instead of
epf->sec_epc when removing from the secondary endpoint controller.

Extend the epc->list_lock coverage and clear either epf->epc or
epf->sec_epc as indicated.

Link: https://lore.kernel.org/r/20241107-epc_rfc-v2-2-da5b6a99a66f@quicinc.com
Fixes: 63840ff ("PCI: endpoint: Add support to associate secondary EPC with EPF")
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[mani: reworded subject and description]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Cc: stable@vger.kernel.org

Author: Zijun Hu

drivers/pci/endpoint/pci-epc-core.c

@@ -746,18 +746,18 @@ void pci_epc_remove_epf(struct pci_epc *epc, struct pci_epf *epf,
 	if (IS_ERR_OR_NULL(epc) || !epf)
 		return;
 
+	mutex_lock(&epc->list_lock);
 	if (type == PRIMARY_INTERFACE) {
 		func_no = epf->func_no;
 		list = &epf->list;
+		epf->epc = NULL;
 	} else {
 		func_no = epf->sec_epc_func_no;
 		list = &epf->sec_epc_list;
+		epf->sec_epc = NULL;
 	}
-
-	mutex_lock(&epc->list_lock);
 	clear_bit(func_no, &epc->function_num_map);
 	list_del(list);
-	epf->epc = NULL;
 	mutex_unlock(&epc->list_lock);
 }
 EXPORT_SYMBOL_GPL(pci_epc_remove_epf);