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 D2FBFC352AA for ; Mon, 7 Oct 2019 11:37:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9710821721 for ; Mon, 7 Oct 2019 11:37:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570448233; bh=DeDtg5BYyoH5R50tZVdT+sUkRN+LeIt0NG34SdtAwG8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=QPI/pUakMk5SqHArtHYCo8+bSpWMquO/Rry0x57CCk7vzunAS5P1OCIcIXEP+RSx2 Rd6WIjRP0i4xijgOa5Jbm0+bj33FqNhn8DSAHQJxwcd2xC2JCr8UdcqNPsCNwrCfUT fP+Mv2DzDrfkrDyZHrNJc1UuohyDsMoDEp7yeC5E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727685AbfJGLhN (ORCPT ); Mon, 7 Oct 2019 07:37:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:48546 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727394AbfJGLhM (ORCPT ); Mon, 7 Oct 2019 07:37:12 -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 E6C7FAE65; Mon, 7 Oct 2019 11:37:10 +0000 (UTC) Date: Mon, 7 Oct 2019 13:37:10 +0200 From: Michal Hocko To: Qian Cai Cc: akpm@linux-foundation.org, sergey.senozhatsky.work@gmail.com, pmladek@suse.com, rostedt@goodmis.org, peterz@infradead.org, david@redhat.com, john.ogness@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() Message-ID: <20191007113710.GH2381@dhcp22.suse.cz> References: <20191007080742.GD2381@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 Mon 07-10-19 07:04:00, Qian Cai wrote: > > > > On Oct 7, 2019, at 4:07 AM, Michal Hocko wrote: > > > > I do not think that removing the printk is the right long term solution. > > While I do agree that removing the debugging printk __offline_isolated_pages > > does make sense because it is essentially of a very limited use, this > > doesn't really solve the underlying problem. There are likely other > > printks from zone->lock. It would be much more saner to actually > > disallow consoles to allocate any memory while printk is called from an > > atomic context. > > No, there is only a handful of places called printk() from > zone->lock. It is normal that the callers will quietly process > “struct zone” modification in a short section with zone->lock > held. It is extremely error prone to have any zone->lock vs. printk dependency. I do not want to play an endless whack a mole. > No, it is not about “allocate any memory while printk is called from an > atomic context”. It is opposite lock chain from different processors which has the same effect. For example, > > CPU0: CPU1: CPU2: > console_owner > sclp_lock > sclp_lock zone_lock > zone_lock > console_owner Why would sclp_lock ever take a zone->lock (apart from an allocation). So really if sclp_lock is a lock that might be taken from many contexts and generate very subtle lock dependencies then it should better be really careful what it is calling into. In other words you are trying to fix a wrong end of the problem. Fix the console to not allocate or depend on MM by other means. -- Michal Hocko SUSE Labs