[PATCH -mm 0/1] signal: simplify set_user_sigmask/restore_user_sigmask

[Oleg Nesterov <oleg@redhat.com>]

On top of

	signal-remove-the-wrong-signal_pending-check-in-restore_user_sigmask.patch

Let me repeat, every file touched by this patch needs more cleanups,
fs/aio.c looks wrong with or without the recent changes. Lets discuss
this later.

To simplify the review, please see the code with this patch applied.
I am using epoll_pwait() as an example because it looks very simple.

Note that this patch moves WARN_ON(!TIF_SIGPENDING) from set_restore_sigmask()
to restore_unless().

	int set_user_sigmask(const sigset_t __user *umask, size_t sigsetsize)
	{
		sigset_t *kmask;

		if (!umask)
			return 0;
		if (sigsetsize != sizeof(sigset_t))
			return -EINVAL;
		if (copy_from_user(kmask, umask, sizeof(sigset_t)))
			return -EFAULT;

		set_restore_sigmask();
		current->saved_sigmask = current->blocked;
		set_current_blocked(kmask);

		return 0;
	}

	static inline void restore_saved_sigmask_unless(bool interrupted)
	{
		if (interrupted)
			WARN_ON(!test_thread_flag(TIF_SIGPENDING));
		else
			restore_saved_sigmask();
	}

	SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
			int, maxevents, int, timeout, const sigset_t __user *, sigmask,
			size_t, sigsetsize)
	{
		int error;

		/*
		 * If the caller wants a certain signal mask to be set during the wait,
		 * we apply it here.
		 */
		error = set_user_sigmask(sigmask, sigsetsize);
		if (error)
			return error;

		error = do_epoll_wait(epfd, events, maxevents, timeout);
		restore_saved_sigmask_unless(error == -EINTR);

		return error;
	}

Oleg.