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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 91C39C4360C for ; Tue, 8 Oct 2019 13:37:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68273206C0 for ; Tue, 8 Oct 2019 13:37:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570541850; bh=Yi9JCPbELBiVusSY2wzUw0dhpptkn0LIP1Ap2KhWFME=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=oWXLjvdB82WRRuQ9JUGkee/tCkXLww7WD9gdLcCsSPHEptMncwwfPqvQX2gqmao9K JXcBF5xOZ6QvmqxkF2s1fDmWIF/o3zsrJv2QdJWyoWAdbxvvzmC9Y4tVrRNKXJsvyM bDw3Tem8KPSKeBe2ud17EbMhcP6rqSnYc2c/Bw10= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726043AbfJHNh3 (ORCPT ); Tue, 8 Oct 2019 09:37:29 -0400 Received: from mx2.suse.de ([195.135.220.15]:41526 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725917AbfJHNh3 (ORCPT ); Tue, 8 Oct 2019 09:37:29 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 0BC46B021; Tue, 8 Oct 2019 13:37:28 +0000 (UTC) Date: Tue, 8 Oct 2019 15:37:27 +0200 From: Michal Hocko To: Qian Cai Cc: Petr Mladek , akpm@linux-foundation.org, sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org, peterz@infradead.org, linux-mm@kvack.org, john.ogness@linutronix.de, david@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() Message-ID: <20191008133727.GK6681@dhcp22.suse.cz> References: <20191008103907.GE6681@dhcp22.suse.cz> <3836DE34-9DD2-4815-9E1E-CB87D881B9AD@lca.pw> <20191008123920.GI6681@dhcp22.suse.cz> <1570539989.5576.295.camel@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1570539989.5576.295.camel@lca.pw> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 08-10-19 09:06:29, Qian Cai wrote: > On Tue, 2019-10-08 at 14:39 +0200, Michal Hocko wrote: > > On Tue 08-10-19 08:00:43, Qian Cai wrote: > > > > > > > > > > On Oct 8, 2019, at 6:39 AM, Michal Hocko wrote: > > > > > > > > Have you actually triggered any real deadlock? With a zone->lock in > > > > place it would be pretty clear with hard lockups detected. > > > > > > Yes, I did trigger here and there, and those lockdep splats are > > > especially useful to figure out why. > > > > Can you provide a lockdep splat from an actual deadlock please? I am > > sorry but your responses tend to be really cryptic and I never know when > > you are talking about actual deadlocks and lockdep splats. I have asked > > about the former several times never receiving a specific answer. > > It is very time-consuming to confirm a lockdep splat is 100% matching a deadlock > giving that it is not able to reproduce on will yet, so when I did encounter a > memory offline deadlock where "echo offline > memory/state" just hang, but there > is no hard lockup probably because the hard lockup detector did not work > properly for some reasons or it keep trying to acquire a spin lock that only > keep the CPU 100%. If there is a real deadlock due to zone->lock then you would certainly get a hard lockup splat. So I strongly suspect that you are seeing a completely different problem. Most likely some pages cannot be migrated and the offlining code will retry for ever. You can terminate that from the userspace by a fatal signal of course. -- Michal Hocko SUSE Labs