From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750969Ab2D2EMM (ORCPT ); Sun, 29 Apr 2012 00:12:12 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:35838 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750744Ab2D2EML (ORCPT ); Sun, 29 Apr 2012 00:12:11 -0400 Date: Sun, 29 Apr 2012 05:12:05 +0100 From: Al Viro To: Martin Schwidefsky Cc: Oleg Nesterov , Linus Torvalds , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC] TIF_NOTIFY_RESUME, arch/*/*/*signal*.c and all such Message-ID: <20120429041205.GY6871@ZenIV.linux.org.uk> References: <20120424072617.GB6871@ZenIV.linux.org.uk> <20120426183742.GA324@redhat.com> <20120426231942.GJ6871@ZenIV.linux.org.uk> <20120427172444.GA30267@redhat.com> <20120427184528.GL6871@ZenIV.linux.org.uk> <20120427202002.8ED632C0BF@topped-with-meat.com> <20120427211244.GO6871@ZenIV.linux.org.uk> <20120427212729.652542C0AF@topped-with-meat.com> <20120427231526.GP6871@ZenIV.linux.org.uk> <20120427233235.GQ6871@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120427233235.GQ6871@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 28, 2012 at 12:32:35AM +0100, Al Viro wrote: > On Sat, Apr 28, 2012 at 12:15:26AM +0100, Al Viro wrote: > > > I think all such architectures need that check lifted to do_notify_resume() > > (and the rest needs it killed, of course). Including x86, by the look > > of it - we _probably_ can't get there with TIF_NOTIFY_RESUME and > > !user_mode(regs), but I'm not entirely sure of that. arm is in about the > > same situation; alpha, ppc{32,64}, sparc{32,64} and m68k really can't get > > there like that (they all check it in the asm glue). mips probably might, > > unless I'm misreading their ret_from_fork()... Fun. > > Speaking of user_mode() oddities - may I politely inquire what had > been smoked to inspire this (in arch/s390/kernel/signal.c): > /* This is the legacy signal stack switching. */ > else if (!user_mode(regs) && > !(ka->sa.sa_flags & SA_RESTORER) && > ka->sa.sa_restorer) { > sp = (unsigned long) ka->sa.sa_restorer; > } > especially when all paths leading to that come through do_signal() that does > if (!user_mode(regs)) > return; > on the same regs. It had been like that since 2.3.99pre8 when s390 went > into the tree... It looks vaguely similar to i386 > /* This is the legacy signal stack switching. */ > if ((regs->ss & 0xffff) != __USER_DS && > !(ka->sa.sa_flags & SA_RESTORER) && > ka->sa.sa_restorer) > sp = (unsigned long) ka->sa.sa_restorer; > but there the code is at least not unreachable... While we are at it, can we *ever* reach do_signal() (nevermind deep in its guts) with !user_mode(regs)? AFAICS, for 31bit possible paths are: do_signal() <- sysc_sigpending <- sysc_work <- sysc_tif, having checked for user_mode(%r11) <- io_sigpending <- io_work_tif <- io_work_user <- io_work, having checked for user_mode(%r11) and identical for 64bit. *All* paths into do_signal() go through tm __PT_PSW+1(%r11),0x01 # returning to user ? and proceed towards do_signal() only if the bit is set. Which is precisely what user_mode(%r11) is... What the hell is going on in that code?