Index: nfsclient/nfs_bio.c
===================================================================
--- nfsclient/nfs_bio.c	(revision 225295)
+++ nfsclient/nfs_bio.c	(working copy)
@@ -1203,6 +1204,7 @@
 		 * to turn off caching in this case.  Very odd.  XXX
 		 */
 		if ((ioflag & IO_SYNC)) {
+			bp->b_flags |= B_SYNC;
 			if (ioflag & IO_INVAL)
 				bp->b_flags |= B_NOCACHE;
 			error = bwrite(bp);
@@ -1659,10 +1680,10 @@
 		uiop->uio_rw = UIO_WRITE;
 		nfsstats.write_bios++;
 
-		if ((bp->b_flags & (B_ASYNC | B_NEEDCOMMIT | B_NOCACHE | B_CLUSTER)) == B_ASYNC)
+		if (!(bp->b_flags & (B_SYNC | B_NEEDCOMMIT | B_NOCACHE | B_CLUSTER)))
 		    iomode = NFSV3WRITE_UNSTABLE;
 		else
 		    iomode = NFSV3WRITE_FILESYNC;
 
 		error = (nmp->nm_rpcops->nr_writerpc)(vp, uiop, cr, &iomode, &must_commit);
 
Index: kern/vfs_bio.c
===================================================================
--- kern/vfs_bio.c	(revision 225284)
+++ kern/vfs_bio.c	(working copy)
@@ -1482,7 +1482,8 @@
 	if (bp->b_bufsize || bp->b_kvasize)
 		bufspacewakeup();
 
-	bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF | B_DIRECT);
+	bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF | B_DIRECT |
+	    B_SYNC);
 	if ((bp->b_flags & B_DELWRI) == 0 && (bp->b_xflags & BX_VNDIRTY))
 		panic("brelse: not dirty");
 	/* unlock */
@@ -1526,7 +1527,7 @@
 				BO_UNLOCK(bo);
 			mtx_unlock(&bqlock);
 		}
-		bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF);
+		bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF | B_SYNC);
 		BUF_UNLOCK(bp);
 		return;
 	}
@@ -1588,7 +1589,7 @@
 	if (bp->b_bufsize && !(bp->b_flags & B_DELWRI))
 		bufspacewakeup();
 
-	bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF);
+	bp->b_flags &= ~(B_ASYNC | B_NOCACHE | B_AGE | B_RELBUF | B_SYNC);
 	if ((bp->b_flags & B_DELWRI) == 0 && (bp->b_xflags & BX_VNDIRTY))
 		panic("bqrelse: not dirty");
 	/* unlock */
Index: fs/nfsclient/nfs_clbio.c
===================================================================
--- fs/nfsclient/nfs_clbio.c	(revision 225284)
+++ fs/nfsclient/nfs_clbio.c	(working copy)
@@ -1207,6 +1207,7 @@
 		 * to turn off caching in this case.  Very odd.  XXX
 		 */
 		if ((ioflag & IO_SYNC)) {
+			bp->b_flags |= B_SYNC;
 			if (ioflag & IO_INVAL)
 				bp->b_flags |= B_NOCACHE;
 			error = bwrite(bp);
@@ -1664,7 +1665,7 @@
 		uiop->uio_rw = UIO_WRITE;
 		NFSINCRGLOBAL(newnfsstats.write_bios);
 
-		if ((bp->b_flags & (B_ASYNC | B_NEEDCOMMIT | B_NOCACHE | B_CLUSTER)) == B_ASYNC)
+		if (!(bp->b_flags & (B_SYNC | B_NEEDCOMMIT | B_NOCACHE | B_CLUSTER)))
 		    iomode = NFSWRITE_UNSTABLE;
 		else
 		    iomode = NFSWRITE_FILESYNC;
Index: sys/buf.h
===================================================================
--- sys/buf.h	(revision 225284)
+++ sys/buf.h	(working copy)
@@ -202,7 +202,7 @@
 #define	B_PERSISTENT	0x00000100	/* Perm. ref'ed while EXT2FS mounted. */
 #define	B_DONE		0x00000200	/* I/O completed. */
 #define	B_EINTR		0x00000400	/* I/O was interrupted */
-#define	B_00000800	0x00000800	/* Available flag. */
+#define	B_SYNC		0x00000800	/* Synchronous write (in NFS). */
 #define	B_00001000	0x00001000	/* Available flag. */
 #define	B_INVAL		0x00002000	/* Does not contain valid info. */
 #define	B_00004000	0x00004000	/* Available flag. */