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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,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 7B976C55191 for ; Thu, 19 Mar 2020 23:28:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 52EBB2076C for ; Thu, 19 Mar 2020 23:28:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727731AbgCSX1w (ORCPT ); Thu, 19 Mar 2020 19:27:52 -0400 Received: from mail.kernel.org ([198.145.29.99]:36588 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727447AbgCSX1e (ORCPT ); Thu, 19 Mar 2020 19:27:34 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id DCD24214DB; Thu, 19 Mar 2020 23:27:33 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.93) (envelope-from ) id 1jF4ZY-000h91-QO; Thu, 19 Mar 2020 19:27:32 -0400 Message-Id: <20200319232732.672722739@goodmis.org> User-Agent: quilt/0.65 Date: Thu, 19 Mar 2020 19:22:27 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Andrew Morton , Peter Zijlstra , Masami Hiramatsu , Alexei Starovoitov , Peter Wu , Jonathan Corbet , Tom Zanussi , Shuah Khan , bpf Subject: [PATCH 08/12 v2] ring-buffer: Optimize rb_iter_head_event() References: <20200319232219.446480829@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Steven Rostedt (VMware)" As it is fine to perform several "peeks" of event data in the ring buffer via the iterator before moving it forward, do not re-read the event, just return what was read before. Otherwise, it can cause inconsistent results, especially when testing multiple CPU buffers to interleave them. Link: http://lkml.kernel.org/r/20200317213416.592032170@goodmis.org Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/ring_buffer.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 475338fda969..5979327254f9 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1929,6 +1929,9 @@ rb_iter_head_event(struct ring_buffer_iter *iter) unsigned long commit; unsigned length; + if (iter->head != iter->next_event) + return iter->event; + /* * When the writer goes across pages, it issues a cmpxchg which * is a mb(), which will synchronize with the rmb here. -- 2.25.1