nvme-pci: check for NULL return from pci_alloc_p2pmem()

Modify nvme_alloc_sq_cmds() to call pci_free_p2pmem() to free the memory
it allocated using pci_alloc_p2pmem() in case pci_p2pmem_virt_to_bus()
returns null.

Makes sure not to call pci_free_p2pmem() if pci_alloc_p2pmem() returned
NULL, which can happen if CONFIG_PCI_P2PDMA is not configured.

The current implementation is not expected to leak since
pci_p2pmem_virt_to_bus() is expected to fail only if pci_alloc_p2pmem()
returns null. However, checking the return value of pci_alloc_p2pmem()
is more explicit.
Signed-off-by: Alan Mikhak <alan.mikhak@sifive.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/pci.c

@@ -1439,11 +1439,15 @@ static int nvme_alloc_sq_cmds(struct nvme_dev *dev, struct nvme_queue *nvmeq,
 
 	if (qid && dev->cmb_use_sqes && (dev->cmbsz & NVME_CMBSZ_SQS)) {
 		nvmeq->sq_cmds = pci_alloc_p2pmem(pdev, SQ_SIZE(depth));
-		nvmeq->sq_dma_addr = pci_p2pmem_virt_to_bus(pdev,
-						nvmeq->sq_cmds);
-		if (nvmeq->sq_dma_addr) {
-			set_bit(NVMEQ_SQ_CMB, &nvmeq->flags);
-			return 0; 
+		if (nvmeq->sq_cmds) {
+			nvmeq->sq_dma_addr = pci_p2pmem_virt_to_bus(pdev,
+							nvmeq->sq_cmds);
+			if (nvmeq->sq_dma_addr) {
+				set_bit(NVMEQ_SQ_CMB, &nvmeq->flags);
+				return 0;
+			}
+
+			pci_free_p2pmem(pdev, nvmeq->sq_cmds, SQ_SIZE(depth));
 		}
 	}