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 7B1EEC4332F for ; Wed, 18 May 2022 18:18:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241354AbiERSSl (ORCPT ); Wed, 18 May 2022 14:18:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54258 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241443AbiERSSe (ORCPT ); Wed, 18 May 2022 14:18:34 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id EF0731BDAC6 for ; Wed, 18 May 2022 11:18:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652897897; h=from:from:reply-to:subject:subject: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=10OqHV6ywZ9TQP4XYR0/v4q26hWVHGE57ElgvBgOhDI=; b=fm5G3zTRyF6ezHyeANM7Y2qZH6GU9kttPoLxzAKCWyGtUX1zVGc3SqrouKd1BqvCYQvyTa 6hxUm4IUTOsHLFFnuWnrV3vxW4c14QGF+UXC+Jebehf6hz2KtJQqgL93YXO96vkZgG1EGf pvtHAJPM4s1G+RaZ2moCGuxp1BnwVt8= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-45-VlvN4W8jOBykXg8-dtuYIw-1; Wed, 18 May 2022 14:18:14 -0400 X-MC-Unique: VlvN4W8jOBykXg8-dtuYIw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2D5893C6053A; Wed, 18 May 2022 18:18:08 +0000 (UTC) Received: from redhat.com (unknown [10.22.16.62]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ED7C41410F36; Wed, 18 May 2022 18:18:07 +0000 (UTC) Date: Wed, 18 May 2022 14:18:06 -0400 From: Joe Lawrence To: live-patching@vger.kernel.org Cc: Miroslav Benes , Petr Mladek , 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> X-Scanned-By: MIMEDefang 2.85 on 10.11.54.7 Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Wed, May 18, 2022 at 01:34:24PM -0400, 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? Or should we just > drop the msg altogether to avoid the situation? I don't think it's > absolutely necessary for the tests. > > [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. > + */ > 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); > + wait_for_completion(&busymod_work_started); > > if (!block_transition) { > /* > -- > 2.26.3 > [ fixup ycote's email address, sorry Yannick :D ] -- Joe