NFSv4.1: Remove redundant reference to the pnfs_layout_hdr

Each layout segment already holds a reference to the pnfs_layout_hdr,
so there is no need to hold an extra reference that is released once
the last layout segment is freed.

Ensure that pnfs_find_alloc_layout() always returns a reference
to the pnfs_layout_hdr, which will be matched by the final call to
pnfs_put_layout_hdr() in pnfs_update_layout().
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/pnfs.c

@@ -331,11 +331,8 @@ pnfs_layout_remove_lseg(struct pnfs_layout_hdr *lo,
 
 	WARN_ON(test_bit(NFS_LSEG_VALID, &lseg->pls_flags));
 	list_del_init(&lseg->pls_list);
-	if (list_empty(&lo->plh_segs)) {
+	if (list_empty(&lo->plh_segs))
 		set_bit(NFS_LAYOUT_DESTROYED, &lo->plh_flags);
-		/* Matched by initial refcount set in alloc_init_layout_hdr */
-		pnfs_put_layout_hdr_locked(lo);
-	}
 	rpc_wake_up(&NFS_SERVER(inode)->roc_rpcwaitq);
 }
 
@@ -468,8 +465,7 @@ pnfs_mark_matching_lsegs_invalid(struct pnfs_layout_hdr *lo,
 	dprintk("%s:Begin lo %p\n", __func__, lo);
 
 	if (list_empty(&lo->plh_segs)) {
-		if (!test_and_set_bit(NFS_LAYOUT_DESTROYED, &lo->plh_flags))
-			pnfs_put_layout_hdr_locked(lo);
+		set_bit(NFS_LAYOUT_DESTROYED, &lo->plh_flags);
 		return 0;
 	}
 	list_for_each_entry_safe(lseg, next, &lo->plh_segs, pls_list)
@@ -929,7 +925,7 @@ pnfs_find_alloc_layout(struct inode *ino,
 	if (nfsi->layout) {
 		if (test_bit(NFS_LAYOUT_DESTROYED, &nfsi->layout->plh_flags))
 			return NULL;
-		else
+		pnfs_get_layout_hdr(nfsi->layout);
 		return nfsi->layout;
 	}
 	spin_unlock(&ino->i_lock);
@@ -1129,7 +1125,6 @@ pnfs_update_layout(struct inode *ino,
 		goto out_unlock;
 	atomic_inc(&lo->plh_outstanding);
 
-	pnfs_get_layout_hdr(lo);
 	if (list_empty(&lo->plh_segs))
 		first = true;