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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 4033EC4361B for ; Wed, 16 Dec 2020 09:27:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C81D5230FF for ; Wed, 16 Dec 2020 09:27:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725885AbgLPJ1j (ORCPT ); Wed, 16 Dec 2020 04:27:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49932 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725820AbgLPJ1j (ORCPT ); Wed, 16 Dec 2020 04:27:39 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2A3EAC0613D6; Wed, 16 Dec 2020 01:26:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=VNK0Q94OzG6UefHS8Pno57bJJDEcOK4GilOJyawPb2U=; b=SpYqwyf6Cd7HJkTZSGadOIuGsx coZSqaI65Eh5jOb0e32VAw6wuVu7tG+cx8fsrcvmKI9kfqC/R4jqbfSb/IjwXSlH0FaGkvZCR+lMy kwIjRq2OgKr4rUyU4Ij+a2KsFiwBFrDKQQYuft4ocu/1wSmAO2p6GJCpx0f2OK+CMbXf0YUd3up6X 2fe+LFi0AaSfjBvBdHtqDgEOlD4F/DZ+p/Rz2HzGjIhgOOX0hL+b29Q5c+zqy0UsQgsDV/tGrufwq jXBRd4r7CUu+R2yGws+0oDMM/9wDS4CmPNR70AgWzSQZwRzQ55zMKV+KDFLmcsompocxmdi7qYVeS 0F81reMw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kpT5C-0000cB-Ju; Wed, 16 Dec 2020 09:26:54 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 7CB02304D28; Wed, 16 Dec 2020 10:26:49 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CC8C22CADD8D4; Wed, 16 Dec 2020 10:26:49 +0100 (CET) Date: Wed, 16 Dec 2020 10:26:49 +0100 From: Peter Zijlstra To: Dexuan Cui Cc: Ingo Molnar , Daniel Bristot de Oliveira , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , jeyu@kernel.org, Josh Poimboeuf Subject: Re: static_branch_enable() does not work from a __init function? Message-ID: <20201216092649.GM3040@hirez.programming.kicks-ass.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 16, 2020 at 03:54:29AM +0000, Dexuan Cui wrote: > Hi, > The below init_module() prints "foo: false". This is strange since > static_branch_enable() is called before the static_branch_unlikely(). > This strange behavior happens to v5.10 and an old v5.4 kernel. > > If I remove the "__init" marker from the init_module() function, then > I get the expected output of "foo: true"! I guess here I'm missing > something with Static Keys? *groan*... I think this is because __init is ran with MODULE_STATE_COMING, we only switch to MODULE_STATE_LIVE later. Let me see if there's a sane way to untangle that. > #include > #include > #include > > static DEFINE_STATIC_KEY_FALSE(enable_foo); > > int __init init_module(void) > { > static_branch_enable(&enable_foo); > > if (static_branch_unlikely(&enable_foo)) > printk("foo: true\n"); > else > printk("foo: false\n"); > > return 0; > } > > void cleanup_module(void) > { > static_branch_disable(&enable_foo); > } > > MODULE_LICENSE("GPL"); > > > PS, I originally found: in arch/x86/kvm/vmx/vmx.c: vmx_init(), it looks > like the line "static_branch_enable(&enable_evmcs);" does not take effect > in a v5.4-based kernel, but does take effect in the v5.10 kernel in the > same x86-64 virtual machine on Hyper-V, so I made the above test module > to test static_branch_enable(), and found that static_branch_enable() in > the test module does not work with both v5.10 and my v5.4 kernel, if the > __init marker is used. > > Thanks, > -- Dexuan > >