NFS: Set an attribute barrier on all updates

Ensure that we update the attribute barrier even if there were no
invalidations, provided that this value is newer than the old one.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Tested-by: Chuck Lever <chuck.lever@oracle.com>
diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index 3a2d127d..299bf71 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -1738,6 +1738,7 @@
 		nfs_inc_stats(inode, NFSIOS_ATTRINVALIDATE);
 		nfsi->attrtimeo = NFS_MINATTRTIMEO(inode);
 		nfsi->attrtimeo_timestamp = now;
+		/* Set barrier to be more recent than all outstanding updates */
 		nfsi->attr_gencount = nfs_inc_attr_generation_counter();
 	} else {
 		if (!time_in_range_open(now, nfsi->attrtimeo_timestamp, nfsi->attrtimeo_timestamp + nfsi->attrtimeo)) {
@@ -1745,6 +1746,9 @@
 				nfsi->attrtimeo = NFS_MAXATTRTIMEO(inode);
 			nfsi->attrtimeo_timestamp = now;
 		}
+		/* Set the barrier to be more recent than this fattr */
+		if ((long)fattr->gencount - (long)nfsi->attr_gencount > 0)
+			nfsi->attr_gencount = fattr->gencount;
 	}
 	invalid &= ~NFS_INO_INVALID_ATTR;
 	/* Don't invalidate the data if we were to blame */