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 860866B0388 for ; Mon, 20 Mar 2017 17:30:16 -0400 (EDT) Received: by mail-lf0-f69.google.com with SMTP id p85so79636193lfg.5 for ; Mon, 20 Mar 2017 14:30:16 -0700 (PDT) Received: from cloudserver094114.home.net.pl (cloudserver094114.home.net.pl. [79.96.170.134]) by mx.google.com with ESMTPS id l198si10058324lfe.22.2017.03.20.14.30.14 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 20 Mar 2017 14:30:14 -0700 (PDT) From: "Rafael J. Wysocki" Subject: Re: memory hotplug and force_remove Date: Mon, 20 Mar 2017 22:24:42 +0100 Message-ID: <2735706.OR0SQDpVy6@aspire.rjw.lan> In-Reply-To: <20170320192938.GA11363@dhcp22.suse.cz> References: <20170320192938.GA11363@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 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. 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