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=-2.5 required=3.0 tests=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 21E0DC10F14 for ; Tue, 8 Oct 2019 13:37:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E5202206C0 for ; Tue, 8 Oct 2019 13:37:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E5202206C0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 609EB8E0005; Tue, 8 Oct 2019 09:37:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5BA5D8E0003; Tue, 8 Oct 2019 09:37:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4D06B8E0005; Tue, 8 Oct 2019 09:37:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0226.hostedemail.com [216.40.44.226]) by kanga.kvack.org (Postfix) with ESMTP id 254DA8E0003 for ; Tue, 8 Oct 2019 09:37:30 -0400 (EDT) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id CC6FA181AC9B4 for ; Tue, 8 Oct 2019 13:37:29 +0000 (UTC) X-FDA: 76020719418.01.rain41_7b9996f198f09 X-HE-Tag: rain41_7b9996f198f09 X-Filterd-Recvd-Size: 2830 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Tue, 8 Oct 2019 13:37:29 +0000 (UTC) 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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