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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 CA829C43381 for ; Mon, 4 Mar 2019 21:50:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9CA0720823 for ; Mon, 4 Mar 2019 21:50:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726452AbfCDVuD (ORCPT ); Mon, 4 Mar 2019 16:50:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:51626 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726069AbfCDVuD (ORCPT ); Mon, 4 Mar 2019 16:50:03 -0500 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 3B889206B6; Mon, 4 Mar 2019 21:50:02 +0000 (UTC) Date: Mon, 4 Mar 2019 16:50:00 -0500 From: Steven Rostedt To: Tom Zanussi Cc: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Tom Zanussi , Namhyung Kim Subject: Re: [PATCH 2/2] tracing: Use strncpy instead of memcpy for string keys in hist triggers Message-ID: <20190304165000.0ce0fbdd@gandalf.local.home> In-Reply-To: <50c35ae1267d64eee975b8125e151e600071d4dc.1549309756.git.tom.zanussi@linux.intel.com> References: <50c35ae1267d64eee975b8125e151e600071d4dc.1549309756.git.tom.zanussi@linux.intel.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 4 Feb 2019 15:07:24 -0600 Tom Zanussi wrote: > From: Tom Zanussi > > Because there may be random garbage beyond a string's null terminator, > it's not correct to copy the the complete character array for use as a > hist trigger key. This results in multiple histogram entries for the > 'same' string key. > > So, in the case of a string key, use strncpy instead of memcpy to > avoid copying in the extra bytes. > > Before, using the gdbus entries in the following hist trigger as an > example: > > # echo 'hist:key=comm' > /sys/kernel/debug/tracing/events/sched/sched_waking/trigger > # cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist > > ... > > { comm: ImgDecoder #4 } hitcount: 203 > { comm: gmain } hitcount: 213 > { comm: gmain } hitcount: 216 > { comm: StreamTrans #73 } hitcount: 221 > { comm: mozStorage #3 } hitcount: 230 > { comm: gdbus } hitcount: 233 > { comm: StyleThread#5 } hitcount: 253 > { comm: gdbus } hitcount: 256 > { comm: gdbus } hitcount: 260 > { comm: StyleThread#4 } hitcount: 271 > > ... > > # cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist | egrep gdbus | wc -l > 51 > > After: > > # cat /sys/kernel/debug/tracing/events/sched/sched_waking/hist | egrep gdbus | wc -l > 1 > > Signed-off-by: Tom Zanussi > Cc: Namhyung Kim > --- > kernel/trace/trace_events_hist.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c > index c4a667503bf0..1b349689b897 100644 > --- a/kernel/trace/trace_events_hist.c > +++ b/kernel/trace/trace_events_hist.c > @@ -4695,9 +4695,10 @@ static inline void add_to_key(char *compound_key, void *key, > /* ensure NULL-termination */ > if (size > key_field->size - 1) > size = key_field->size - 1; > - } > > - memcpy(compound_key + key_field->offset, key, size); > + strncpy(compound_key + key_field->offset, (char *)key, size); > + } else > + memcpy(compound_key + key_field->offset, key, size); > } > Shouldn't we use strncpy() in save_comm() too. Feels safer. -- Steve