From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752658AbbLUXGv (ORCPT ); Mon, 21 Dec 2015 18:06:51 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:42089 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751659AbbLUXGu (ORCPT ); Mon, 21 Dec 2015 18:06:50 -0500 Date: Mon, 21 Dec 2015 15:06:49 -0800 From: Andrew Morton To: Vitaly Kuznetsov Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tang Chen , Naoya Horiguchi , Xishi Qiu , Sheng Yong , David Rientjes , Zhu Guihua , Dan Williams , David Vrabel , Igor Mammedov Subject: Re: [PATCH] memory-hotplug: don't BUG() in register_memory_resource() Message-Id: <20151221150649.f385889426082059bfc09495@linux-foundation.org> In-Reply-To: <8737uwt8hw.fsf@vitty.brq.redhat.com> References: <1450450224-18515-1-git-send-email-vkuznets@redhat.com> <20151218145022.eae1e368c82f090900582fcc@linux-foundation.org> <8737uwt8hw.fsf@vitty.brq.redhat.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 21 Dec 2015 11:13:15 +0100 Vitaly Kuznetsov wrote: > Andrew Morton writes: > > > On Fri, 18 Dec 2015 15:50:24 +0100 Vitaly Kuznetsov wrote: > > > >> Out of memory condition is not a bug and while we can't add new memory in > >> such case crashing the system seems wrong. Propagating the return value > >> from register_memory_resource() requires interface change. > >> > >> --- a/mm/memory_hotplug.c > >> +++ b/mm/memory_hotplug.c > >> +static int register_memory_resource(u64 start, u64 size, > >> + struct resource **resource) > >> { > >> struct resource *res; > >> res = kzalloc(sizeof(struct resource), GFP_KERNEL); > >> - BUG_ON(!res); > >> + if (!res) > >> + return -ENOMEM; > >> > >> res->name = "System RAM"; > >> res->start = start; > >> @@ -140,9 +142,10 @@ static struct resource *register_memory_resource(u64 start, u64 size) > >> if (request_resource(&iomem_resource, res) < 0) { > >> pr_debug("System RAM resource %pR cannot be added\n", res); > >> kfree(res); > >> - res = NULL; > >> + return -EEXIST; > >> } > >> - return res; > >> + *resource = res; > >> + return 0; > >> } > > > > Was there a reason for overwriting the request_resource() return > > value? > > Ordinarily it should be propagated back to callers. > > > > Please review. > > > > This is a nice-to-have addition but it will break at least ACPI > memhotplug: request_resource() has the following: > > conflict = request_resource_conflict(root, new); > return conflict ? -EBUSY : 0; > > so we'll end up returning -EBUSY from register_memory_resource() and > add_memory(), at the same time acpi_memory_enable_device() counts on > -EEXIST: > > result = add_memory(node, info->start_addr, info->length); > > /* > * If the memory block has been used by the kernel, add_memory() > * returns -EEXIST. If add_memory() returns the other error, it > * means that this memory block is not used by the kernel. > */ > if (result && result != -EEXIST) > continue; > > So I see 3 options here: > 1) Keep the overwrite > 2) Change the request_resource() return value to -EEXIST > 3) Adapt all add_memory() call sites to -EBUSY. > > Please let me know your preference. urgh, what a mess. We should standardize on EBUSY or EEXIST, I don't see that it matter much which is chosen. And for robustness the callers should be checking for (err < 0) unless there's a very good reason otherwise. But it doesn't seem terribly important.