When the volume is being downgraded from a read-write mode, mark

it as clean.

PR:		kern/85366
Submitted by:	Dan Lukes <dan at obluda dot cz>
MFC After:	2 weeks

sys/fs/msdosfs/msdosfs_vfsops.c

@@ -283,6 +283,10 @@ msdosfs_mount(struct mount *mp, struct thread *td)
 			g_access(pmp->pm_cp, 0, -1, 0);
 			g_topology_unlock();
 			PICKUP_GIANT();
+			/* Now the volume is clean. Mark it. */
+			error = markvoldirty(pmp, 0);
+			if (error && (flags & FORCECLOSE) == 0)
+				return (error);
 		} else if ((pmp->pm_flags & MSDOSFSMNT_RONLY) &&
 		    !vfs_flagopt(mp->mnt_optnew, "ro", NULL, 0)) {
 			/*