From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB5C3C46471 for ; Tue, 7 Aug 2018 09:10:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AAA7C2089C for ; Tue, 7 Aug 2018 09:10:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AAA7C2089C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387643AbeHGLXe (ORCPT ); Tue, 7 Aug 2018 07:23:34 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:52312 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726414AbeHGLXe (ORCPT ); Tue, 7 Aug 2018 07:23:34 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id AEBEE402242D; Tue, 7 Aug 2018 09:10:11 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id 94B772166BA2; Tue, 7 Aug 2018 09:10:09 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 7 Aug 2018 11:10:11 +0200 (CEST) Date: Tue, 7 Aug 2018 11:10:08 +0200 From: Oleg Nesterov To: Jiri Olsa Cc: Jiri Olsa , Arnaldo Carvalho de Melo , Milind Chabbi , lkml , Ingo Molnar , Namhyung Kim , David Ahern , Alexander Shishkin , Peter Zijlstra , Frederic Weisbecker Subject: Re: [PATCH 3/2] perf/hw_breakpoint: Remove superfluous bp->attr.disabled = 0 new attr has disabled set Message-ID: <20180807091008.GA19831@redhat.com> References: <20180806101241.6444-1-jolsa@kernel.org> <20180806101241.6444-3-jolsa@kernel.org> <20180806124839.GC7840@redhat.com> <20180806132353.GA7463@krava> <20180806150836.GD16446@krava> <20180806163436.GH7840@redhat.com> <20180807081616.GB7716@krava> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180807081616.GB7716@krava> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Tue, 07 Aug 2018 09:10:11 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Tue, 07 Aug 2018 09:10:11 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'oleg@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/07, Jiri Olsa wrote: > > On Mon, Aug 06, 2018 at 06:34:36PM +0200, Oleg Nesterov wrote: > > > --- a/kernel/events/hw_breakpoint.c > > > +++ b/kernel/events/hw_breakpoint.c > > > @@ -526,10 +526,9 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att > > > if (err) > > > return err; > > > > > > - if (!attr->disabled) { > > > + if (!attr->disabled) > > > perf_event_enable(bp); > > > - bp->attr.disabled = 0; > > > - } > > > + > > > > Yes, but again, this still looks confusing. > > > > IMO, we should either remove "bp->attr.disabled = attr->disabled" in > > modify_user_hw_breakpoint_check() because bp->attr.disabled is not really > > used, or we should set bp->attr.disabled = 1 on failure just for consistency. > > > > > > Hmm... actually ptrace_get_dr7() checks ->attr.disabled, so we can hit > > WARN_ON(second_pass) in ptrace_write_dr7() in case when attr.disabled is > > falsely 0 because modify_user_hw_breakpoint_check() failed before? > > hum, I can't see how modify_user_hw_breakpoint_check could falsely set disabled > new attr stuff is copied once all checks passed Hmm. So modify_user_hw_breakpoint() does perf_event_disable(bp) first and afaics this doesn't set bp->attr.disabled = 1. If modify_user_hw_breakpoint_check() fails after that we do not update bp->attr, so bp->attr.disabled is still zero while this bp is actually disabled. Again, afaics the core perf code doesn't actually use bp->attr.disabled after perf_event__state_init(). But this can confuse ptrace_write_dr7/ptrace_get_dr7. No? I am on Linus's tree, but I see the same logic in https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/tree/kernel/events/hw_breakpoint.c?h=perf/core Oleg.