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=-13.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLACK,USER_AGENT_SANE_1 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 CF0E6C4727D for ; Tue, 22 Sep 2020 22:00:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D5E820735 for ; Tue, 22 Sep 2020 22:00:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600812045; bh=VzrZMpqwNjj7GLA1FO+ZBXW3i0yjDRa5NIGJNS+NvyI=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=dKD9kw7brRvQLrvHXyhvtjqklYpamFvUO9qImCwM1jY0NlQjwpOVnnwWmbxW3JR/9 wRIh6TAKapelN5XjMi/sIe62302f2UA02WfSvlgBGlP61kwKA0h6GDl/22LwyE8YWY AWf9ThtFNtv5yoCksLddtxY0Wdg1xLKqQIyZ2TeM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726685AbgIVWAo (ORCPT ); Tue, 22 Sep 2020 18:00:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:43960 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726179AbgIVWAo (ORCPT ); Tue, 22 Sep 2020 18:00:44 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (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 78073206B5; Tue, 22 Sep 2020 22:00:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600812043; bh=VzrZMpqwNjj7GLA1FO+ZBXW3i0yjDRa5NIGJNS+NvyI=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=dqj/BZXLnAj8fYN4lRmi2+zahTBkQ6eqj7HhJGcc5HTzUJKxjyvLBsf25w9LHt3wC dX8vKdn6kfDAg0y1Qwp9tVai72L3sll6+i0lbfQ7D4FqINkfOkXQbB9kCznxZFvzIi 138hF0hp5I+/qoyKXhx7BuZlJSKDHxaUdKzUDOu0= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 2120135227BD; Tue, 22 Sep 2020 15:00:43 -0700 (PDT) Date: Tue, 22 Sep 2020 15:00:43 -0700 From: "Paul E. McKenney" To: Alexey Kardashevskiy Cc: rcu@vger.kernel.org, Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , Steven Rostedt , linux-kernel@vger.kernel.org Subject: Re: [PATCH kernel] srcu: Fix static initialization Message-ID: <20200922220043.GF29330@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200908144306.33355-1-aik@ozlabs.ru> <20200909115010.GG29330@paulmck-ThinkPad-P72> <37f76aac-d8e3-8ab1-24e9-c417b719e2a6@ozlabs.ru> <20200910185353.GS29330@paulmck-ThinkPad-P72> <611a6a87-f673-c5b7-3b60-58805fba580a@ozlabs.ru> <20200911135208.GX29330@paulmck-ThinkPad-P72> <20200916161224.GA30546@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 22, 2020 at 10:41:37AM +1000, Alexey Kardashevskiy wrote: > > > On 17/09/2020 02:12, Paul E. McKenney wrote: > > On Fri, Sep 11, 2020 at 06:52:08AM -0700, Paul E. McKenney wrote: > >> On Fri, Sep 11, 2020 at 03:09:41PM +1000, Alexey Kardashevskiy wrote: > >>> On 11/09/2020 04:53, Paul E. McKenney wrote: > >>>> On Wed, Sep 09, 2020 at 10:31:03PM +1000, Alexey Kardashevskiy wrote: > > > > [ . . . ] > > > >>>>> init_srcu_struct_nodes() assumes ssp->sda!=NULL but alloc_percpu() fails > >>>>> here: > >>>>> > >>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/percpu.c#n1734 > >>>>> === > >>>>> } else if (mutex_lock_killable(&pcpu_alloc_mutex)) { > >>>>> pcpu_memcg_post_alloc_hook(objcg, NULL, 0, size); > >>>>> return NULL; > >>>>> === > >>>>> > >>>>> I am still up to reading that osr-rcuusage.pdf to provide better > >>>>> analysis :) Thanks, > >>>> > >>>> Ah, got it! Does the following patch help? > >>>> > >>>> There will likely also need to be changes to cleanup_srcu_struct(), > >>>> but first let's see if I understand the problem. ;-) > >>>> > >>>> Thanx, Paul > >>>> > >>>> ------------------------------------------------------------------------ > >>>> > >>>> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > >>>> index c13348e..6f7880a 100644 > >>>> --- a/kernel/rcu/srcutree.c > >>>> +++ b/kernel/rcu/srcutree.c > >>>> @@ -177,11 +177,13 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) > >>>> INIT_DELAYED_WORK(&ssp->work, process_srcu); > >>>> if (!is_static) > >>>> ssp->sda = alloc_percpu(struct srcu_data); > >>>> + if (!ssp->sda) > >>>> + return -ENOMEM; > >>>> init_srcu_struct_nodes(ssp, is_static); > >>>> ssp->srcu_gp_seq_needed_exp = 0; > >>>> ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); > >>>> smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */ > >>> > >>> The line above confuses me a bit. What you propose returns without > >>> smp_store_release() called which should not matter I suppose. > >> > >> The idea is that if init_srcu_struct() returns -ENOMEM, the structure > >> has not been initialized and had better not be used. If the calling code > >> cannot handle that outcome, then the calling code needs to do something > >> to insulate init_srcu_struct() from signals. One thing that it could > >> do would be to invoke init_srcu_struct() from a workqueue handler and > >> wait for this handler to complete. > >> > >> Please keep in mind that there is nothing init_srcu_struct() can do > >> about this: The srcu_struct is useless unless alloc_percpu() succeeds. > >> > >> And yes, I do need to update the header comments to make this clear. > >> > >>> Otherwise it should work, although I cannot verify right now as my box > >>> went down and since it is across Pacific - it may take time to power > >>> cycle it :) Thanks, > >> > >> I know that feeling! And here is hoping that the box is out of reach > >> of the local hot spots. ;-) > > > > Just following up... Did that patch help? > > Yes it did. > > Tested-by: Alexey Kardashevskiy Thank you, and I will apply on the next rebase. Thanx, Paul