rbd: use GFP_NOIO consistently for request allocations

As of 5a60e876, RBD object request
allocations are made via rbd_obj_request_create() with GFP_NOIO.
However, subsequent OSD request allocations in rbd_osd_req_create*()
use GFP_ATOMIC.

With heavy page cache usage (e.g. OSDs running on same host as krbd
client), rbd_osd_req_create() order-1 GFP_ATOMIC allocations have been
observed to fail, where direct reclaim would have allowed GFP_NOIO
allocations to succeed.

Cc: stable@vger.kernel.org # 3.18+
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Neil Brown <neilb@suse.com>
Signed-off-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

drivers/block/rbd.c

@@ -1953,7 +1953,7 @@ static struct ceph_osd_request *rbd_osd_req_create(
 
 	osdc = &rbd_dev->rbd_client->client->osdc;
 	osd_req = ceph_osdc_alloc_request(osdc, snapc, num_ops, false,
-					  GFP_ATOMIC);
+					  GFP_NOIO);
 	if (!osd_req)
 		return NULL;	/* ENOMEM */
 
@@ -2002,7 +2002,7 @@ rbd_osd_req_create_copyup(struct rbd_obj_request *obj_request)
 	rbd_dev = img_request->rbd_dev;
 	osdc = &rbd_dev->rbd_client->client->osdc;
 	osd_req = ceph_osdc_alloc_request(osdc, snapc, num_osd_ops,
-						false, GFP_ATOMIC);
+						false, GFP_NOIO);
 	if (!osd_req)
 		return NULL;	/* ENOMEM */
 
@@ -2504,7 +2504,7 @@ static int rbd_img_request_fill(struct rbd_img_request *img_request,
 					bio_chain_clone_range(&bio_list,
 								&bio_offset,
 								clone_size,
-								GFP_ATOMIC);
+								GFP_NOIO);
 			if (!obj_request->bio_list)
 				goto out_unwind;
 		} else if (type == OBJ_REQUEST_PAGES) {