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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AAD88C433F5 for ; Mon, 18 Oct 2021 21:50:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F6EE60E78 for ; Mon, 18 Oct 2021 21:50:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232659AbhJRVxD (ORCPT ); Mon, 18 Oct 2021 17:53:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:38270 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229524AbhJRVxB (ORCPT ); Mon, 18 Oct 2021 17:53:01 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 067F861027; Mon, 18 Oct 2021 21:50:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634593849; bh=mLgSi2xtumYxIqCbU67hwJSn6yVpStslxKRIS+tQIzs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DdSkjgxB9oOTLqp/1F0fEAopdX4rZqp1oWHFr9sGNB+uY42tawsW/+Cb3l0irjVxr pOVX9i7CUZARocInWWf48lnPm2zkkr5JpWcxrEvxo5ofmB2YOP77JAIS4DPRrV7+oM EK7IFeqI4I0+KYpztLbGJ+kXALY4uGEeBluetFOgdgg8yCa4ZYJ6BvFlVfush5TGrw 7Hky3usbubYYyf/N02/f8HkTe0FxJ8sFl6WFBpuUvZFkTDxcHb4eRaobexv1/DNjN4 X8wqfKqpUvbSCiz4VBYBxIrBb0O+DghUkCaqhYPXP7rW7Zm/amJpZnDhSQbDnUG+Og rl1IkAoZGUCTg== Date: Mon, 18 Oct 2021 23:50:46 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: LKML , Uladzislau Rezki , Boqun Feng , Neeraj Upadhyay , Josh Triplett , Joel Fernandes , rcu@vger.kernel.org Subject: Re: [PATCH] rcu/nocb: Fix misordered rcu_barrier() while (de-)offloading Message-ID: <20211018215046.GA453817@lothringen> References: <20211018113259.450292-1-frederic@kernel.org> <20211018161814.GS880162@paulmck-ThinkPad-P17-Gen-1> <20211018174242.GA450204@lothringen> <20211018183604.GT880162@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211018183604.GT880162@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 18, 2021 at 11:36:04AM -0700, Paul E. McKenney wrote: > On Mon, Oct 18, 2021 at 07:42:42PM +0200, Frederic Weisbecker wrote: > > I think you're right. The real issue is something I wanted to > > fix next: RCU_SEGCBLIST_RCU_CORE isn't cleared when nocb is enabled on > > boot so rcu_core() always run concurrently with nocb kthreads in TREE04, > > without holding rcu_barrier mutex of course (I mean with the latest patchset). > > That would do it! > > > Ok forget this patch, I'm testing again with simply clearing > > RCU_SEGCBLIST_RCU_CORE on boot. > > Sounds good, looking forward to it! So yes that was indeed the real issue. I've pushed an "rcu/rt-v3" branch which is the same as your dev.2021.10.07a branch but the first patch "rcu/nocb: Prepare state machine for a new step" has this added: diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 3b470113ae38..2461fe8d0c23 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -1171,8 +1171,8 @@ void __init rcu_init_nohz(void) if (rcu_segcblist_empty(&rdp->cblist)) rcu_segcblist_init(&rdp->cblist); rcu_segcblist_offload(&rdp->cblist, true); - rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB); - rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_GP); + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_RCU_CORE); } rcu_organize_nocb_kthreads(); } I still see the oom though, hopefully my series just makes an existing problem more likely to happen. Thanks.