PCI: endpoint: Add missing NULL check for alloc_workqueue()

alloc_workqueue() can return NULL on memory allocation failure. Without
proper error checking, this may lead to a NULL pointer dereference when
queue_work() is later called with the NULL workqueue pointer in
epf_ntb_epc_init().

Add a NULL check immediately after alloc_workqueue() and return -ENOMEM on
failure to prevent the driver from loading with an invalid workqueue
pointer.

Fixes: e35f56b ("PCI: endpoint: Support NTB transfer between RC and EP")
Fixes: 8b821cf ("PCI: endpoint: Add EP function driver to provide NTB functionality")
Signed-off-by: Haotian Zhang <vulab@iscas.ac.cn>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20251110040446.2065-1-vulab@iscas.ac.cn

Author: ISCAS-Vulab

drivers/pci/endpoint/functions/pci-epf-ntb.c

@@ -2126,6 +2126,11 @@ static int __init epf_ntb_init(void)
 
 	kpcintb_workqueue = alloc_workqueue("kpcintb",
 				    WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_PERCPU, 0);
+	if (!kpcintb_workqueue) {
+		pr_err("Failed to allocate kpcintb workqueue\n");
+		return -ENOMEM;
+	}
+
 	ret = pci_epf_register_driver(&epf_ntb_driver);
 	if (ret) {
 		destroy_workqueue(kpcintb_workqueue);

drivers/pci/endpoint/functions/pci-epf-vntb.c

@@ -1653,6 +1653,11 @@ static int __init epf_ntb_init(void)
 
 	kpcintb_workqueue = alloc_workqueue("kpcintb",
 				    WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_PERCPU, 0);
+	if (!kpcintb_workqueue) {
+		pr_err("Failed to allocate kpcintb workqueue\n");
+		return -ENOMEM;
+	}
+
 	ret = pci_epf_register_driver(&epf_ntb_driver);
 	if (ret) {
 		destroy_workqueue(kpcintb_workqueue);