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=-13.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 827B0C64E7B for ; Sat, 28 Nov 2020 21:56:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5B880208D5 for ; Sat, 28 Nov 2020 21:56:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391585AbgK1V4S (ORCPT ); Sat, 28 Nov 2020 16:56:18 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:52857 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387745AbgK1U5d (ORCPT ); Sat, 28 Nov 2020 15:57:33 -0500 Received: from mail-wr1-f71.google.com ([209.85.221.71]) by youngberry.canonical.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1kiwK8-0007lg-OT for linux-kernel@vger.kernel.org; Sat, 28 Nov 2020 09:15:20 +0000 Received: by mail-wr1-f71.google.com with SMTP id u8so2696551wrq.6 for ; Sat, 28 Nov 2020 01:15:20 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:mime-version :content-disposition; bh=L1ZVOdz/CkW3cEUwY2qKMVfD+NLZGHncisYT77s+qT8=; b=oVYRQuWltJcTTmumydnIY27G1Jv5lZtBHd+byVayls/ztLJo2MYbz/gRB94lPMskyh wVkvGnmYoENThOlwtUWh+rdqeV2xFevaAFFfLzYKHBvHtPF+UTC+BPXHKEYxSG8oLAda mn9kmh9nIrK8bIPHkthPEyviXufy0Ljnt20uGU/Hn/Rjalslygqnr8/cj5dLapUxC0xY jZ7/MB2OoIiReI7ELCXY9NqtomFHPPECqjbI/xLhx7v27KSVmZWIaZNqfqTo95HzBDta kL1aqgOdflH1wHzbeXvhE584xz22/UIxKZ01+9xD77gzp/OkTWRwc8sDMSmQxBXOSpNS 8Jbw== X-Gm-Message-State: AOAM530/rAslLfHFhJRKSbCv8reMVzVMr8Rl8D/coY/xj2DGWHxCETgU JnidtR+b6lvs81A8lSskFjFUdqS3Fx4w40XbKtMg64VfRSIk7Bs7tQ40tZ2XqrW/Sgj1AiVlWaJ 648opJIM6zgwz3pj20UUMWdM6Cbe+QnUXl6h9GWa1nw== X-Received: by 2002:adf:a451:: with SMTP id e17mr15976269wra.99.1606554920349; Sat, 28 Nov 2020 01:15:20 -0800 (PST) X-Google-Smtp-Source: ABdhPJxnKnNbHi8CC875wCyQhrcSim8L++P0BQn8wvxEhd6w3P0570zKFSnlyCCs+yqoJ1SS3sWyYQ== X-Received: by 2002:adf:a451:: with SMTP id e17mr15976260wra.99.1606554920140; Sat, 28 Nov 2020 01:15:20 -0800 (PST) Received: from localhost (host-79-35-122-236.retail.telecomitalia.it. [79.35.122.236]) by smtp.gmail.com with ESMTPSA id d16sm20573195wrw.17.2020.11.28.01.15.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 28 Nov 2020 01:15:19 -0800 (PST) Date: Sat, 28 Nov 2020 10:15:17 +0100 From: Andrea Righi To: Steven Rostedt Cc: Ingo Molnar , Masami Hiramatsu , linux-kernel@vger.kernel.org Subject: [PATCH] ring-buffer: set the right timestamp in the slow path of __rb_reserve_next() Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In the slow path of __rb_reserve_next() a nested event(s) can happen between evaluating the timestamp delta of the current event and updating write_stamp via local_cmpxchg(); in this case the delta is not valid anymore and it should be set to 0 (same timestamp as the interrupting event), since the event that we are currently processing is not the last event in the buffer. Link: https://lwn.net/Articles/831207 Fixes: a389d86f7fd0 ("ring-buffer: Have nested events still record running time stamp") Signed-off-by: Andrea Righi --- kernel/trace/ring_buffer.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index dc83b3fa9fe7..5e30e0cdb6ce 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -3287,11 +3287,11 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer, ts = rb_time_stamp(cpu_buffer->buffer); barrier(); /*E*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) && - info->after < ts) { + info->after < ts && + rb_time_cmpxchg(&cpu_buffer->write_stamp, + info->after, info->ts)) { /* Nothing came after this event between C and E */ info->delta = ts - info->after; - (void)rb_time_cmpxchg(&cpu_buffer->write_stamp, - info->after, info->ts); info->ts = ts; } else { /* -- 2.29.2