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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 278FDC433EF for ; Mon, 23 May 2022 15:29:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237988AbiEWP3F (ORCPT ); Mon, 23 May 2022 11:29:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237958AbiEWP3C (ORCPT ); Mon, 23 May 2022 11:29:02 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2EFC55F24A for ; Mon, 23 May 2022 08:28:57 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id C52B821ADF; Mon, 23 May 2022 15:28:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1653319735; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=Jem8FhQW836UK+ykeN9QiCIY1SDpyQ0+Kmk2n3rFb8k=; b=PzD31psqZiMHtmL4hpLVuA2q1udh3VLX/R7tcI1nZM3mTxij5/y29Bp0UmtF3Hr03uh18s KENm5SvqIW0DY9iuMb0306jBTXaNZhOUmdrBA2WfPZtcCjmG/MydCeOHQiWWw5RiE9a9j9 iTSZ0nQsdbDasJAuKbLZug2eEd+Aorw= Received: from suse.cz (unknown [10.100.208.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id A55972C141; Mon, 23 May 2022 15:28:55 +0000 (UTC) Date: Mon, 23 May 2022 17:28:55 +0200 From: Petr Mladek To: Joe Lawrence Cc: live-patching@vger.kernel.org, Miroslav Benes , Yannick Cote Subject: Re: [PATCH] selftests/livepatch: better synchronize test_klp_callbacks_busy Message-ID: References: <20220518173424.911649-1-joe.lawrence@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220518173424.911649-1-joe.lawrence@redhat.com> Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Wed 2022-05-18 13:34:24, Joe Lawrence wrote: > The test_klp_callbacks_busy module conditionally blocks a future > livepatch transition by busy waiting inside its workqueue function, > busymod_work_func(). After scheduling this work, a test livepatch is > loaded, introducing the transition under test. > > Both events are marked in the kernel log for later verification, but > there is no synchronization to ensure that busymod_work_func() logs its > function entry message before subsequent selftest commands log their own > messages. This can lead to a rare test failure due to unexpected > ordering like: > > --- expected > +++ result > @@ -1,7 +1,7 @@ > % modprobe test_klp_callbacks_busy block_transition=Y > test_klp_callbacks_busy: test_klp_callbacks_busy_init > -test_klp_callbacks_busy: busymod_work_func enter > % modprobe test_klp_callbacks_demo > +test_klp_callbacks_busy: busymod_work_func enter > livepatch: enabling patch 'test_klp_callbacks_demo' > livepatch: 'test_klp_callbacks_demo': initializing patching transition > test_klp_callbacks_demo: pre_patch_callback: vmlinux > > Force the module init function to wait until busymod_work_func() has > started (and logged its message), before exiting to the next selftest > steps. > > Fixes: 547840bd5ae5 ("selftests/livepatch: simplify test-klp-callbacks busy target tests") > Signed-off-by: Joe Lawrence > --- > > Hi Petr, I remember you discouraged against a completion variable the > first time around [1], but is there any better way with the workqueue > API to ensure our "enter" message gets logged first? I think that the code was more complicated at that time. Or I have got used to it ;-) > Or should we just drop the msg altogether to avoid the situation? > I don't think it's absolutely necessary for the tests. IMHO, the message helps to make sure that the timing is correct. I would keep it. > [1] https://lore.kernel.org/live-patching/20200602081654.GI27273@linux-b0ei/ > > lib/livepatch/test_klp_callbacks_busy.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/lib/livepatch/test_klp_callbacks_busy.c b/lib/livepatch/test_klp_callbacks_busy.c > index 7ac845f65be5..eb502b2bb3ef 100644 > --- a/lib/livepatch/test_klp_callbacks_busy.c > +++ b/lib/livepatch/test_klp_callbacks_busy.c > @@ -16,10 +16,16 @@ MODULE_PARM_DESC(block_transition, "block_transition (default=false)"); > > static void busymod_work_func(struct work_struct *work); > static DECLARE_WORK(work, busymod_work_func); > +static DECLARE_COMPLETION(busymod_work_started); > > static void busymod_work_func(struct work_struct *work) > { > + /* > + * Hold the init function from exiting until we've started and > + * announced our appearence in the kernel log. > + */ This message would make more sense above the wait_for_completion(). The wait function holds the init function. I would remove the comment here. > pr_info("%s enter\n", __func__); > + complete(&busymod_work_started); > > while (READ_ONCE(block_transition)) { > /* > @@ -36,6 +42,7 @@ static int test_klp_callbacks_busy_init(void) > { > pr_info("%s\n", __func__); > schedule_work(&work); Instead, I would add here something like: /* * Hold the init function from exiting until the message * about entering the busy loop is printed. */ > + wait_for_completion(&busymod_work_started); > > if (!block_transition) { > /* > -- > 2.26.3 With the updated message: Reviewed-by: Petr Mladek Best Regards, Petr PS: I am sorry for the late review. I have busy times.