NFSv4.1/pNFS: Fix a race in initiate_file_draining()

Peng Tao points out that the call to pnfs_mark_matching_lsegs_return()
could race with pnfs_put_lseg(), in which case the layout segment is
cleared, but no layoutreturn will be sent.
Fix is to replace the call to pnfs_mark_matching_lsegs_invalid().
Reported-by: NPeng Tao <tao.peng@primarydata.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/callback_proc.c

@@ -216,11 +216,8 @@ static u32 initiate_file_draining(struct nfs_client *clp,
 		goto unlock;
 	}
 
-	if (pnfs_mark_matching_lsegs_invalid(lo, &free_me_list,
+	if (pnfs_mark_matching_lsegs_return(lo, &free_me_list,
 					&args->cbl_range)) {
-		pnfs_mark_matching_lsegs_return(lo,
-				&free_me_list,
-				&args->cbl_range);
 		rv = NFS4_OK;
 		goto unlock;
 	}