Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752532AbbKGLSe (ORCPT ); Sat, 7 Nov 2015 06:18:34 -0500 Received: from mail.skyhub.de ([78.46.96.112]:44647 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751093AbbKGLSd (ORCPT ); Sat, 7 Nov 2015 06:18:33 -0500 Date: Sat, 7 Nov 2015 12:18:24 +0100 From: Borislav Petkov To: Andy Lutomirski Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Brian Gerst , Linus Torvalds , =?utf-8?B?RnLDqWTDqXJpYw==?= Weisbecker , Peter Zijlstra Subject: Re: [PATCH 1/4] x86/entry/64: Fix irqflag tracing wrt context tracking Message-ID: <20151107111824.GA6137@pd.tnic> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1402 Lines: 35 On Fri, Nov 06, 2015 at 03:12:43PM -0800, Andy Lutomirski wrote: > Paolo pointed out that enter_from_user_mode could be called while > irqflags were traced as though IRQs were on. > > In principle, this could confuse lockdep. It doesn't cause any > problems that I've seen in any configuration, but if I build with > CONFIG_DEBUG_LOCKDEP=y, enable a nohz_full CPU, and add code like: > > if (irqs_disabled()) { > spin_lock(&something); > spin_unlock(&something); > } > > to the top of enter_from_user_mode, then lockdep will complain > without this fix. It seems that lockdep's irqflags sanity checks > are too weak to detect this bug without forcing the issue. > > This patch adds one byte to normal kernels, and it's IMO a bit ugly. > I haven't spotted a better way to do this yet, though. The issue is > that we can't do TRACE_IRQS_OFF until after SWAPGS (if needed), but > we're also supposed to do it before calling C code. I would not mind to have that explanation in the code itself so that people don't scratch heads why the duplicated TRACE_IRQS_OFF call. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/