From patchwork Thu Oct 10 08:35:37 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 11182973 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 547071709 for ; Thu, 10 Oct 2019 08:58:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 360AB21D80 for ; Thu, 10 Oct 2019 08:58:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570697916; bh=RGbsMYw9+rLEFO5N8Q1T3vut1c+0zUuAmpw9zyAiwcw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=LREe/6/agcc4mr3EB5BJi7mOGe44ySa45+ZkYlvvez7a56+/a07z545Qv0LGD9ZPd s1hsIFR1eyt89YlL3QjCM7SM77Qc9FnVIyNmA96Is6Gr3j4No3no5euMgy9Ey5fVBn vaWKk4M0kcy/O7HKz03T0rdDZ9TJKeTvL0ZEMEMM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389165AbfJJIph (ORCPT ); Thu, 10 Oct 2019 04:45:37 -0400 Received: from mail.kernel.org ([198.145.29.99]:51220 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387614AbfJJIpg (ORCPT ); Thu, 10 Oct 2019 04:45:36 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 20482218AC; Thu, 10 Oct 2019 08:45:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570697135; bh=RGbsMYw9+rLEFO5N8Q1T3vut1c+0zUuAmpw9zyAiwcw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=q0SgKqVO98vP3a/VG8zKQgL8PrUZI5lYxiHkpPoOwvpSkMztle2euKgp9ZCbBD5+u C4iw6nrm42UkhR7e7v77dddH+5rH+lLqo5Oq8h3IVsflg40JrIsxurlL9Yl5Ve+Pc4 LGCyJRL35D7hYWG+gONFg/gND8sbXhnOfci7cNMQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Linux Trace Devel , linux-rt-users , "Steven Rostedt (VMware)" , Tom Zanussi Subject: [PATCH 4.19 030/114] tracing: Make sure variable reference alias has correct var_ref_idx Date: Thu, 10 Oct 2019 10:35:37 +0200 Message-Id: <20191010083559.568035880@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191010083544.711104709@linuxfoundation.org> References: <20191010083544.711104709@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: linux-trace-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-trace-devel@vger.kernel.org From: Tom Zanussi commit 17f8607a1658a8e70415eef67909f990d13017b5 upstream. Original changelog from Steve Rostedt (except last sentence which explains the problem, and the Fixes: tag): I performed a three way histogram with the following commands: echo 'irq_lat u64 lat pid_t pid' > synthetic_events echo 'wake_lat u64 lat u64 irqlat pid_t pid' >> synthetic_events echo 'hist:keys=common_pid:irqts=common_timestamp.usecs if function == 0xffffffff81200580' > events/timer/hrtimer_start/trigger echo 'hist:keys=common_pid:lat=common_timestamp.usecs-$irqts:onmatch(timer.hrtimer_start).irq_lat($lat,pid) if common_flags & 1' > events/sched/sched_waking/trigger echo 'hist:keys=pid:wakets=common_timestamp.usecs,irqlat=lat' > events/synthetic/irq_lat/trigger echo 'hist:keys=next_pid:lat=common_timestamp.usecs-$wakets,irqlat=$irqlat:onmatch(synthetic.irq_lat).wake_lat($lat,$irqlat,next_pid)' > events/sched/sched_switch/trigger echo 1 > events/synthetic/wake_lat/enable Basically I wanted to see: hrtimer_start (calling function tick_sched_timer) Note: # grep tick_sched_timer /proc/kallsyms ffffffff81200580 t tick_sched_timer And save the time of that, and then record sched_waking if it is called in interrupt context and with the same pid as the hrtimer_start, it will record the latency between that and the waking event. I then look at when the task that is woken is scheduled in, and record the latency between the wakeup and the task running. At the end, the wake_lat synthetic event will show the wakeup to scheduled latency, as well as the irq latency in from hritmer_start to the wakeup. The problem is that I found this: -0 [007] d... 190.485261: wake_lat: lat=27 irqlat=190485230 pid=698 -0 [005] d... 190.485283: wake_lat: lat=40 irqlat=190485239 pid=10 -0 [002] d... 190.488327: wake_lat: lat=56 irqlat=190488266 pid=335 -0 [005] d... 190.489330: wake_lat: lat=64 irqlat=190489262 pid=10 -0 [003] d... 190.490312: wake_lat: lat=43 irqlat=190490265 pid=77 -0 [005] d... 190.493322: wake_lat: lat=54 irqlat=190493262 pid=10 -0 [005] d... 190.497305: wake_lat: lat=35 irqlat=190497267 pid=10 -0 [005] d... 190.501319: wake_lat: lat=50 irqlat=190501264 pid=10 The irqlat seemed quite large! Investigating this further, if I had enabled the irq_lat synthetic event, I noticed this: -0 [002] d.s. 249.429308: irq_lat: lat=164968 pid=335 -0 [002] d... 249.429369: wake_lat: lat=55 irqlat=249429308 pid=335 Notice that the timestamp of the irq_lat "249.429308" is awfully similar to the reported irqlat variable. In fact, all instances were like this. It appeared that: irqlat=$irqlat Wasn't assigning the old $irqlat to the new irqlat variable, but instead was assigning the $irqts to it. The issue is that assigning the old $irqlat to the new irqlat variable creates a variable reference alias, but the alias creation code forgets to make sure the alias uses the same var_ref_idx to access the reference. Link: http://lkml.kernel.org/r/1567375321.5282.12.camel@kernel.org Cc: Linux Trace Devel Cc: linux-rt-users Cc: stable@vger.kernel.org Fixes: 7e8b88a30b085 ("tracing: Add hist trigger support for variable reference aliases") Reported-by: Steven Rostedt (VMware) Signed-off-by: Tom Zanussi Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace_events_hist.c | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -2526,6 +2526,8 @@ static struct hist_field *create_alias(s return NULL; } + alias->var_ref_idx = var_ref->var_ref_idx; + return alias; }