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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_2 autolearn=unavailable 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 6DBA7C432BE for ; Thu, 12 Aug 2021 14:00:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D82A6108C for ; Thu, 12 Aug 2021 14:00:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237783AbhHLOAm (ORCPT ); Thu, 12 Aug 2021 10:00:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:34290 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232351AbhHLOAj (ORCPT ); Thu, 12 Aug 2021 10:00:39 -0400 Received: from oasis.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 505C76104F; Thu, 12 Aug 2021 14:00:12 +0000 (UTC) Date: Thu, 12 Aug 2021 10:00:10 -0400 From: Steven Rostedt To: Yordan Karadzhov Cc: linux-trace-devel@vger.kernel.org, linux-kernel@vger.kernel.org, Tom Zanussi , Daniel Bristot de Oliveira , Masami Hiramatsu Subject: Re: [PATCH 1/2] libtracefs: Add random number to keep synthetic variables unique Message-ID: <20210812100010.0f3922d1@oasis.local.home> In-Reply-To: <13bed3a6-7e39-eec2-2421-a80081302a81@gmail.com> References: <20210812005546.910833-1-rostedt@goodmis.org> <20210812005546.910833-2-rostedt@goodmis.org> <13bed3a6-7e39-eec2-2421-a80081302a81@gmail.com> X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 12 Aug 2021 11:34:57 +0300 Yordan Karadzhov wrote: > > @@ -957,7 +960,15 @@ static char *new_arg(struct tracefs_synth *synth) > > char *arg; > > int ret; > > > > - ret = asprintf(&arg, "__arg__%d", cnt); > > + /* Create a unique argument name */ > > + if (!synth->arg_name[0]) { > > + srand(time(NULL)); > > Nit: Have in mind that time(NULL) has 1 second resolution. Fast consecutive calls (within a second) of this function can > generate identical random numbers. > This can be mitigated if we do something like this: > > struct timeval now; > > gettimeofday(&now, NULL); > srand(now.tv_usec); So you are saying that if one thread created two synthetic events within a second, then this could give the same value. Yeah, I can see that could happen. I was hoping to avoid the declaring the "now" and calling gettimeofday(). Also, looking more into this, I see that rand() is not safe in thread context (it may not be a problem, but there's no guarantee), and perhaps we should just open code it, to be on the safe side. Thanks for the review. -- Steve