nfs: use credential guards in nfs_local_call_read()

Use credential guards for scoped credential override with automatic
restoration on scope exit.

Link: https://patch.msgid.link/[e-mail]
Reviewed-by: Amir Goldstein <[e-mail]>
Signed-off-by: Christian Brauner <[e-mail]>

fs/nfs/localio.c

···
 	struct nfs_local_kiocb *iocb =
 		container_of(work, struct nfs_local_kiocb, work);
 	struct file *filp = iocb->kiocb.ki_filp;
-	const struct cred *save_cred;
 	ssize_t status;
 
-	save_cred = override_creds(filp->f_cred);
+	scoped_with_creds(filp->f_cred) {
+		for (int i = 0; i < iocb->n_iters ; i++) {
+			if (iocb->iter_is_dio_aligned[i]) {
+				iocb->kiocb.ki_flags |= IOCB_DIRECT;
+				iocb->kiocb.ki_complete = nfs_local_read_aio_complete;
+				iocb->aio_complete_work = nfs_local_read_aio_complete_work;
+			}
 
-	for (int i = 0; i < iocb->n_iters ; i++) {
-		if (iocb->iter_is_dio_aligned[i]) {
-			iocb->kiocb.ki_flags |= IOCB_DIRECT;
-			iocb->kiocb.ki_complete = nfs_local_read_aio_complete;
-			iocb->aio_complete_work = nfs_local_read_aio_complete_work;
-		}
-
-		iocb->kiocb.ki_pos = iocb->offset[i];
-		status = filp->f_op->read_iter(&iocb->kiocb, &iocb->iters[i]);
-		if (status != -EIOCBQUEUED) {
-			nfs_local_pgio_done(iocb->hdr, status);
-			if (iocb->hdr->task.tk_status)
-				break;
+			iocb->kiocb.ki_pos = iocb->offset[i];
+			status = filp->f_op->read_iter(&iocb->kiocb, &iocb->iters[i]);
+			if (status != -EIOCBQUEUED) {
+				nfs_local_pgio_done(iocb->hdr, status);
+				if (iocb->hdr->task.tk_status)
+					break;
+			}
 		}
 	}
-
-	revert_creds(save_cred);
 
 	if (status != -EIOCBQUEUED) {
 		nfs_local_read_done(iocb, status);