From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751409AbbLUKNV (ORCPT ); Mon, 21 Dec 2015 05:13:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54700 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751076AbbLUKNU (ORCPT ); Mon, 21 Dec 2015 05:13:20 -0500 From: Vitaly Kuznetsov To: Andrew Morton 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() References: <1450450224-18515-1-git-send-email-vkuznets@redhat.com> <20151218145022.eae1e368c82f090900582fcc@linux-foundation.org> Date: Mon, 21 Dec 2015 11:13:15 +0100 In-Reply-To: <20151218145022.eae1e368c82f090900582fcc@linux-foundation.org> (Andrew Morton's message of "Fri, 18 Dec 2015 14:50:22 -0800") Message-ID: <8737uwt8hw.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > --- a/mm/memory_hotplug.c~memory-hotplug-dont-bug-in-register_memory_resource-fix > +++ a/mm/memory_hotplug.c > @@ -131,7 +131,9 @@ static int register_memory_resource(u64 > struct resource **resource) > { > struct resource *res; > + int ret = 0; > res = kzalloc(sizeof(struct resource), GFP_KERNEL); > + > if (!res) > return -ENOMEM; > > @@ -139,13 +141,14 @@ static int register_memory_resource(u64 > res->start = start; > res->end = start + size - 1; > res->flags = IORESOURCE_MEM | IORESOURCE_BUSY; > - if (request_resource(&iomem_resource, res) < 0) { > + ret = request_resource(&iomem_resource, res); > + if (ret < 0) { > pr_debug("System RAM resource %pR cannot be added\n", res); > kfree(res); > - return -EEXIST; > + } else { > + *resource = res; > } > - *resource = res; > - return 0; > + return ret; > } > > static void release_memory_resource(struct resource *res) > _ -- Vitaly