From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id 8741C6B0390 for ; Thu, 30 Mar 2017 04:47:55 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id i18so8842555wrb.21 for ; Thu, 30 Mar 2017 01:47:55 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id d204si2959616wme.141.2017.03.30.01.47.53 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 30 Mar 2017 01:47:53 -0700 (PDT) Date: Thu, 30 Mar 2017 10:47:52 +0200 (CEST) From: Jiri Kosina Subject: Re: memory hotplug and force_remove In-Reply-To: <2203902.lsAnRkUs2Y@aspire.rjw.lan> Message-ID: References: <20170320192938.GA11363@dhcp22.suse.cz> <2735706.OR0SQDpVy6@aspire.rjw.lan> <20170328075808.GB18241@dhcp22.suse.cz> <2203902.lsAnRkUs2Y@aspire.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: "Rafael J. Wysocki" Cc: Michal Hocko , Toshi Kani , joeyli , linux-mm@kvack.org, LKML , linux-api@vger.kernel.org On Tue, 28 Mar 2017, Rafael J. Wysocki wrote: > > > > 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. :-) I'd agree with that; at the same time, udev rule should be submitted to systemd folks though. I don't think there is anything existing in this area yet (neither do distros ship their own udev rules for this AFAIK). Thanks, -- Jiri Kosina SUSE Labs -- 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