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 C635DC46460 for ; Thu, 9 Aug 2018 16:30:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8848521EB7 for ; Thu, 9 Aug 2018 16:30:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8848521EB7 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 S1732552AbeHIS4A (ORCPT ); Thu, 9 Aug 2018 14:56:00 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:57614 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730419AbeHISz7 (ORCPT ); Thu, 9 Aug 2018 14:55:59 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 17C417A7EB; Thu, 9 Aug 2018 16:30:20 +0000 (UTC) Received: from krava (ovpn-204-81.brq.redhat.com [10.40.204.81]) by smtp.corp.redhat.com (Postfix) with SMTP id 7BBCA10FFE71; Thu, 9 Aug 2018 16:30:15 +0000 (UTC) Date: Thu, 9 Aug 2018 18:30:15 +0200 From: Jiri Olsa To: Oleg Nesterov Cc: Jiri Olsa , Arnaldo Carvalho de Melo , lkml , Ingo Molnar , Namhyung Kim , David Ahern , Alexander Shishkin , Peter Zijlstra , Milind Chabbi , Frederic Weisbecker Subject: Re: [PATCH 4/5] perf/hw_breakpoint: Set breakpoint as disabled in modify_user_hw_breakpoint error path Message-ID: <20180809163015.GA23170@krava> References: <20180809120305.20693-1-jolsa@kernel.org> <20180809120305.20693-5-jolsa@kernel.org> <20180809141713.GB22636@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180809141713.GB22636@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Thu, 09 Aug 2018 16:30:20 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Thu, 09 Aug 2018 16:30:20 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'jolsa@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 09, 2018 at 04:17:13PM +0200, Oleg Nesterov wrote: > On 08/09, Jiri Olsa wrote: > > > > @@ -523,8 +523,10 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att > > perf_event_disable(bp); > > > > err = modify_user_hw_breakpoint_check(bp, attr, false); > > - if (err) > > + if (err) { > > + bp->attr.disabled = 1; > > return err; > > Yes, but on the second thought... Can't we simply do > > int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr) > { > int err; > > /* > * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it > * will not be possible to raise IPIs that invoke __perf_event_disable. > * So call the function directly after making sure we are targeting the > * current task. > */ > if (irqs_disabled() && bp->ctx && bp->ctx->task == current) > perf_event_disable_local(bp); > else > perf_event_disable(bp); > > err = modify_user_hw_breakpoint_check(bp, attr, false); > > if (!bp.attr->disabled) > perf_event_enable(bp); > > return err; > } > > instead of this and the next patch? > > We can do this because (as you pointed out) validate_hw_breakpoint() has already > gone in -tip tree, and (afaics) modify_user_hw_breakpoint_check() never changes > perf_event's state on failure, so we can safely "restart" this bp if it was enabled > before. > > 1. This is what we had before the recent f67b15037a7a50c57f72e69a6d59941ad90a0f0f > "perf/hwbp: Simplify the perf-hwbp code, fix documentation". > > Note that this commit was actually the bug fix which introduced another problem > fixed by your 2/5. > > But see above, perf_event_enable() is no longer unsafe after > modify_user_hw_breakpoint_check(), we can restore the previous semantics. > > 2. This matches perf_event_modify_breakpoint(). Which btw can be simplified a bit, > it too can simply do > > if (!bp->attr.disabled) > _perf_event_enable(bp); > > return err; yep, seems good.. will send new version thanks, jirka