ceph: fix rsize/wsize capping in ceph_direct_read_write()

rsize/wsize cap should be applied before ceph_osdc_new_request() is
called.  Otherwise, if the size is limited by the cap instead of the
stripe unit, ceph_osdc_new_request() would setup an extent op that is
bigger than what dio_get_pages_alloc() would pin and add to the page
vector, triggering asserts in the messenger.

Cc: stable@vger.kernel.org
Fixes: 95cca2b4 ("ceph: limit osd write size")
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>

fs/ceph/file.c

@@ -918,6 +918,11 @@ ceph_direct_read_write(struct kiocb *iocb, struct iov_iter *iter,
 		size_t start = 0;
 		ssize_t len;
 
+		if (write)
+			size = min_t(u64, size, fsc->mount_options->wsize);
+		else
+			size = min_t(u64, size, fsc->mount_options->rsize);
+
 		vino = ceph_vino(inode);
 		req = ceph_osdc_new_request(&fsc->client->osdc, &ci->i_layout,
 					    vino, pos, &size, 0,
@@ -933,11 +938,6 @@ ceph_direct_read_write(struct kiocb *iocb, struct iov_iter *iter,
 			break;
 		}
 
-		if (write)
-			size = min_t(u64, size, fsc->mount_options->wsize);
-		else
-			size = min_t(u64, size, fsc->mount_options->rsize);
-
 		len = size;
 		pages = dio_get_pages_alloc(iter, len, &start, &num_pages);
 		if (IS_ERR(pages)) {