pnfs: make pnfs_layout_process more robust

It can return NULL if layoutgets are blocked currently. Fix it to return
-EAGAIN in that case, so we can properly handle it in pnfs_update_layout.

Also, clean up and simplify the error handling -- eliminate "status" and
just use "lseg".
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/pnfs.c

@@ -1708,21 +1708,19 @@ pnfs_layout_process(struct nfs4_layoutget *lgp)
 	struct pnfs_layout_segment *lseg;
 	struct inode *ino = lo->plh_inode;
 	LIST_HEAD(free_me);
-	int status = -EINVAL;
 
 	if (!pnfs_sanity_check_layout_range(&res->range))
-		goto out;
+		return ERR_PTR(-EINVAL);
 
 	/* Inject layout blob into I/O device driver */
 	lseg = NFS_SERVER(ino)->pnfs_curr_ld->alloc_lseg(lo, res, lgp->gfp_flags);
-	if (!lseg || IS_ERR(lseg)) {
+	if (IS_ERR_OR_NULL(lseg)) {
 		if (!lseg)
-			status = -ENOMEM;
-		else
-			status = PTR_ERR(lseg);
-		dprintk("%s: Could not allocate layout: error %d\n",
-		       __func__, status);
-		goto out;
+			lseg = ERR_PTR(-ENOMEM);
+
+		dprintk("%s: Could not allocate layout: error %ld\n",
+		       __func__, PTR_ERR(lseg));
+		return lseg;
 	}
 
 	init_lseg(lo, lseg);
@@ -1732,15 +1730,14 @@ pnfs_layout_process(struct nfs4_layoutget *lgp)
 	spin_lock(&ino->i_lock);
 	if (pnfs_layoutgets_blocked(lo)) {
 		dprintk("%s forget reply due to state\n", __func__);
-		goto out_forget_reply;
+		goto out_forget;
 	}
 
 	if (nfs4_stateid_match_other(&lo->plh_stateid, &res->stateid)) {
 		/* existing state ID, make sure the sequence number matches. */
 		if (pnfs_layout_stateid_blocked(lo, &res->stateid)) {
 			dprintk("%s forget reply due to sequence\n", __func__);
-			status = -EAGAIN;
-			goto out_forget_reply;
+			goto out_forget;
 		}
 		pnfs_set_layout_stateid(lo, &res->stateid, false);
 	} else {
@@ -1766,14 +1763,12 @@ pnfs_layout_process(struct nfs4_layoutget *lgp)
 	spin_unlock(&ino->i_lock);
 	pnfs_free_lseg_list(&free_me);
 	return lseg;
-out:
-	return ERR_PTR(status);
 
-out_forget_reply:
+out_forget:
 	spin_unlock(&ino->i_lock);
 	lseg->pls_layout = lo;
 	NFS_SERVER(ino)->pnfs_curr_ld->free_lseg(lseg);
-	goto out;
+	return ERR_PTR(-EAGAIN);
 }
 
 static void