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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS 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 3EE7EC04AA7 for ; Wed, 15 May 2019 06:51:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 137642084E for ; Wed, 15 May 2019 06:51:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726283AbfEOGvK (ORCPT ); Wed, 15 May 2019 02:51:10 -0400 Received: from mga01.intel.com ([192.55.52.88]:57740 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725781AbfEOGvK (ORCPT ); Wed, 15 May 2019 02:51:10 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 May 2019 23:51:10 -0700 X-ExtLoop1: 1 Received: from um.fi.intel.com (HELO localhost) ([10.237.72.63]) by FMSMGA003.fm.intel.com with ESMTP; 14 May 2019 23:51:08 -0700 From: Alexander Shishkin To: Yabin Cui , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Jiri Olsa , Namhyung Kim Cc: linux-kernel@vger.kernel.org, Yabin Cui , alexander.shishkin@linux.intel.com Subject: Re: [PATCH] perf/ring_buffer: Fix exposing a temporarily decreased data_head. In-Reply-To: <20190515003059.23920-1-yabinc@google.com> References: <20190515003059.23920-1-yabinc@google.com> Date: Wed, 15 May 2019 09:51:07 +0300 Message-ID: <87ef50xlb8.fsf@ashishki-desk.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Yabin Cui writes: > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > index 674b35383491..0b9aefe13b04 100644 > --- a/kernel/events/ring_buffer.c > +++ b/kernel/events/ring_buffer.c > @@ -54,8 +54,10 @@ static void perf_output_put_handle(struct perf_output_handle *handle) > * IRQ/NMI can happen here, which means we can miss a head update. > */ > > - if (!local_dec_and_test(&rb->nest)) > + if (local_read(&rb->nest) > 1) { > + local_dec(&rb->nest); What stops rb->nest changing between local_read() and local_dec()? Regards, -- Alex