[PATCH] disable unshare(CLONE_VM) for now

sys_unshare() does mmput(new_mm).  This is not enough if we have
mm->core_waiters.

This patch is a temporary fix for soon to be released 2.6.16.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
[ Checked with Uli: "I'm not planning to use unshare(CLONE_VM).  It's
  not needed for any functionality planned so far.  What we (as in Red
  Hat) need unshare() for now is the filesystem side." ]
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/fork.c

@@ -1478,9 +1478,7 @@ static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)
 
 	if ((unshare_flags & CLONE_VM) &&
 	    (mm && atomic_read(&mm->mm_users) > 1)) {
-		*new_mmp = dup_mm(current);
-		if (!*new_mmp)
-			return -ENOMEM;
+		return -EINVAL;
 	}
 
 	return 0;