From patchwork Thu Mar 19 23:22:27 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 1258512 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: incoming-bpf@patchwork.ozlabs.org Delivered-To: patchwork-incoming-bpf@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (no SPF record) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=bpf-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=goodmis.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 48k3473MLTz9sSX for ; Fri, 20 Mar 2020 10:28:07 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727613AbgCSX1s (ORCPT ); Thu, 19 Mar 2020 19:27:48 -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 Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@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.