From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f69.google.com (mail-lf0-f69.google.com [209.85.215.69]) by kanga.kvack.org (Postfix) with ESMTP id E08D66B0390 for ; Tue, 28 Mar 2017 11:28:41 -0400 (EDT) Received: by mail-lf0-f69.google.com with SMTP id n78so37389356lfi.4 for ; Tue, 28 Mar 2017 08:28:41 -0700 (PDT) Received: from cloudserver094114.home.net.pl (cloudserver094114.home.net.pl. [79.96.170.134]) by mx.google.com with ESMTPS id 9si1559144ljg.235.2017.03.28.08.28.40 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 28 Mar 2017 08:28:40 -0700 (PDT) From: "Rafael J. Wysocki" Subject: Re: memory hotplug and force_remove Date: Tue, 28 Mar 2017 17:22:58 +0200 Message-ID: <2203902.lsAnRkUs2Y@aspire.rjw.lan> In-Reply-To: <20170328075808.GB18241@dhcp22.suse.cz> References: <20170320192938.GA11363@dhcp22.suse.cz> <2735706.OR0SQDpVy6@aspire.rjw.lan> <20170328075808.GB18241@dhcp22.suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Toshi Kani , Jiri Kosina , joeyli , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org On Tuesday, March 28, 2017 09:58:08 AM Michal Hocko wrote: > On Mon 20-03-17 22:24:42, Rafael J. Wysocki wrote: > > On Monday, March 20, 2017 03:29:39 PM Michal Hocko wrote: > > > Hi Rafael, > > > > Hi, > > > > > we have been chasing the following BUG() triggering during the memory > > > hotremove (remove_memory): > > > ret = walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1), NULL, > > > check_memblock_offlined_cb); > > > if (ret) > > > BUG(); > > > > > > and it took a while to learn that the issue is caused by > > > /sys/firmware/acpi/hotplug/force_remove being enabled. I was really > > > surprised to see such an option because at least for the memory hotplug > > > it cannot work at all. Memory hotplug fails when the memory is still > > > in use. Even if we do not BUG() here enforcing the hotplug operation > > > will lead to problematic behavior later like crash or a silent memory > > > corruption if the memory gets onlined back and reused by somebody else. > > > > > > I am wondering what was the motivation for introducing this behavior and > > > whether there is a way to disallow it for memory hotplug. Or maybe drop > > > it completely. What would break in such a case? > > > > Honestly, I don't remember from the top of my head and I haven't looked at > > that code for several months. > > > > I need some time to recall that. > > Did you have any chance to look into this? Well, yes. It looks like that was added for some people who depended on the old behavior at that time. I guess we can try to drop it and see what happpens. :-) Thanks, Rafael -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org