PCI/P2PDMA: fix the gen_pool_add_virt() failure path

The pci_p2pdma_add_resource() implementation immediately frees the pgmap
if gen_pool_add_virt() fails.  However, that means that when @dev
triggers a devres release devm_memremap_pages_release() will crash
trying to access the freed @pgmap.

Use the new devm_memunmap_pages() to manually free the mapping in the
error path.

Link: http://lkml.kernel.org/r/155727337603.292046.13101332703665246702.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>
Fixes: 52916982 ("PCI/P2PDMA: Support peer-to-peer memory")
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/pci/p2pdma.c

@@ -208,13 +208,15 @@ int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
 			pci_bus_address(pdev, bar) + offset,
 			resource_size(&pgmap->res), dev_to_node(&pdev->dev));
 	if (error)
-		goto pgmap_free;
+		goto pages_free;
 
 	pci_info(pdev, "added peer-to-peer DMA memory %pR\n",
 		 &pgmap->res);
 
 	return 0;
 
+pages_free:
+	devm_memunmap_pages(&pdev->dev, pgmap);
 pgmap_free:
 	devm_kfree(&pdev->dev, pgmap);
 	return error;