From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH] Rename is_compat_task to in_compat_syscall
Date: Tue, 19 Jan 2016 21:55:36 +0000
Message-ID: <20160119215535.GU17997@ZenIV.linux.org.uk>
References: <79347eb4ec12be34098b36693bcf613eb597cbe9.1453239942.git.luto@kernel.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-arch-owner@vger.kernel.org>
Received: from zeniv.linux.org.uk ([195.92.253.2]:48541 "EHLO
	ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1757775AbcASVzj (ORCPT
	<rfc822;linux-arch@vger.kernel.org>); Tue, 19 Jan 2016 16:55:39 -0500
Content-Disposition: inline
In-Reply-To: <79347eb4ec12be34098b36693bcf613eb597cbe9.1453239942.git.luto@kernel.org>
Sender: linux-arch-owner@vger.kernel.org
List-ID: <linux-arch.vger.kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Ingo Molnar <mingo@kernel.org>, x86@kernel.org, linux-arch@vger.kernel.org, David Miller <davem@davemloft.net>, linux-s390@vger.kernel.org

On Tue, Jan 19, 2016 at 01:47:24PM -0800, Andy Lutomirski wrote:
> Essentially all users of is_compat_task in the kernel are trying to
> determine whether they are executing in the context of a compat
> syscall.  On at least x86_64 and sparc, these are not at all the
> same question.
> 
> On x86_64 and sparc, therefore, is_compat_task doesn't return the
> overall compat state of the task; it returns true if the task is
> currently in a compat syscall.

The hell it does.  Andy, TIF_32BIT is *NOT* set on syscall entry; it is
set by execve().  And 64bit task (with that bit clear) can bloody well
issue 32bit syscalls.  Really.