From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754826Ab2HAOVY (ORCPT ); Wed, 1 Aug 2012 10:21:24 -0400 Received: from www.linutronix.de ([62.245.132.108]:51289 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754598Ab2HAOVW (ORCPT ); Wed, 1 Aug 2012 10:21:22 -0400 Message-ID: <50193B5C.90404@linutronix.de> Date: Wed, 01 Aug 2012 16:21:16 +0200 From: Sebastian Andrzej Siewior User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.5) Gecko/20120624 Icedove/10.0.5 MIME-Version: 1.0 To: Oleg Nesterov CC: Roland McGrath , "H. Peter Anvin" , linux-kernel@vger.kernel.org, ananth@in.ibm.com, a.p.zijlstra@chello.nl, mingo@redhat.com, srikar@linux.vnet.ibm.com Subject: Re: Q: user_enable_single_step() && update_debugctlmsr() References: <20120730141638.GA5306@redhat.com> <1343735548-18101-1-git-send-email-bigeasy@linutronix.de> <1343735548-18101-2-git-send-email-bigeasy@linutronix.de> <20120731175108.GC14576@redhat.com> <50183273.9070304@linutronix.de> <20120801122616.GA32705@redhat.com> <20120801130118.GA2386@redhat.com> <50192FF5.1060208@linutronix.de> <20120801134652.GA4707@redhat.com> <50193528.3070503@linutronix.de> <20120801140121.GA5333@redhat.com> In-Reply-To: <20120801140121.GA5333@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/01/2012 04:01 PM, Oleg Nesterov wrote: > On 08/01, Sebastian Andrzej Siewior wrote: >> >> On 08/01/2012 03:46 PM, Oleg Nesterov wrote: >> >>>>> But, worse, isn't it wrong? Suppose that debugger switches to >>>>> another TIF_SINGLESTEP&& !TIF_BLOCKSTEP task, in this case >>>>> we "leak" DEBUGCTLMSR_BTF, no? >>>> >>>> __switch_to_xtra() should notice the difference in the TIF_BLOCKSTEP >>>> flag and disable it. >>> >>> And how it can notice the difference if there is no difference? >>> >>> (unless, of course debugger is TIF_BLOCKSTEP'ed). >> >> Yes. enable_step() sets DEBUGCTLMSR_BTF along with TIF_BLOCKSTEP. >> kprobes checks the same flag before touching DEBUGCTLMSR_BTF. > > It seems that you replied to the wrong email or I am confused ;) No I think I replied to the correct one :) enable_step() is the only place for ptrace/debugger which is touching DEBUGCTLMSR_BTF. It always sets DEBUGCTLMSR_BTF and TIF_BLOCKSTEP in sync so why should they both end up different? And once __switch_to_extra() notices that TIF_BLOCKSTEP from the previous task is different from the next task is different, then the CPU flag has to be changed. > Let's ignore kprobes here. done. > > Oleg. > Sebastian