Merge branch 'stacking-fixes' (vfs stacking fixes from Jann)

Merge filesystem stacking fixes from Jann Horn.

* emailed patches from Jann Horn <jannh@google.com>:
  sched: panic on corrupted stack end
  ecryptfs: forbid opening files without mmap handler
  proc: prevent stacking filesystems on top
asmlinkage __visible void __sched schedule_user(void)
{
	/*
	 * If we come here after a random call to set_need_resched(),
	 * or we have been woken up remotely but the IPI has not yet arrived,
	 * we haven't yet exited the RCU idle mode. Do it here manually until
	 * we find a better solution.
	 *
	 * NB: There are buggy callers of this function.  Ideally we
	 * should warn if prev_state != CONTEXT_USER, but that will trigger
	 * too frequently to make sense yet.
	 */
	enum ctx_state prev_state = exception_enter();
	schedule();
	exception_exit(prev_state);
}

asmlinkage __visible void __sched schedule_user(void)
{
	/*
	 * If we come here after a random call to set_need_resched(),
	 * or we have been woken up remotely but the IPI has not yet arrived,
	 * we haven't yet exited the RCU idle mode. Do it here manually until
	 * we find a better solution.
	 *
	 * NB: There are buggy callers of this function.  Ideally we
	 * should warn if prev_state != CONTEXT_USER, but that will trigger
	 * too frequently to make sense yet.
	 */
	enum ctx_state prev_state = exception_enter();
	schedule();
	exception_exit(prev_state);
}
