From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AAB24C48BD6 for ; Tue, 25 Jun 2019 08:27:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 83A00216E3 for ; Tue, 25 Jun 2019 08:27:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730297AbfFYI1L (ORCPT ); Tue, 25 Jun 2019 04:27:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:14979 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730197AbfFYI1K (ORCPT ); Tue, 25 Jun 2019 04:27:10 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E6258307CDD5; Tue, 25 Jun 2019 08:27:09 +0000 (UTC) Received: from [10.36.117.83] (ovpn-117-83.ams2.redhat.com [10.36.117.83]) by smtp.corp.redhat.com (Postfix) with ESMTP id DAB7C600C7; Tue, 25 Jun 2019 08:27:07 +0000 (UTC) Subject: Re: [PATCH v2 1/5] drivers/base/memory: Remove unneeded check in remove_memory_block_devices To: Oscar Salvador Cc: akpm@linux-foundation.org, mhocko@suse.com, dan.j.williams@intel.com, pasha.tatashin@soleen.com, Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190625075227.15193-1-osalvador@suse.de> <20190625075227.15193-2-osalvador@suse.de> <3e820fee-f82f-3336-ff34-31c66dbbbbfe@redhat.com> <0ed2f4ec-cc6f-8b81-46b0-d56d90ac1e86@redhat.com> <20190625080909.GA15394@linux> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190625080909.GA15394@linux> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Tue, 25 Jun 2019 08:27:10 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.06.19 10:09, Oscar Salvador wrote: > On Tue, Jun 25, 2019 at 10:03:31AM +0200, David Hildenbrand wrote: >> On 25.06.19 10:01, David Hildenbrand wrote: >>> On 25.06.19 09:52, Oscar Salvador wrote: >>>> remove_memory_block_devices() checks for the range to be aligned >>>> to memory_block_size_bytes, which is our current memory block size, >>>> and WARNs_ON and bails out if it is not. >>>> >>>> This is the right to do, but we do already do that in try_remove_memory(), >>>> where remove_memory_block_devices() gets called from, and we even are >>>> more strict in try_remove_memory, since we directly BUG_ON in case the range >>>> is not properly aligned. >>>> >>>> Since remove_memory_block_devices() is only called from try_remove_memory(), >>>> we can safely drop the check here. >>>> >>>> To be honest, I am not sure if we should kill the system in case we cannot >>>> remove memory. >>>> I tend to think that WARN_ON and return and error is better. >>> >>> I failed to parse this sentence. >>> >>>> >>>> Signed-off-by: Oscar Salvador >>>> --- >>>> drivers/base/memory.c | 4 ---- >>>> 1 file changed, 4 deletions(-) >>>> >>>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c >>>> index 826dd76f662e..07ba731beb42 100644 >>>> --- a/drivers/base/memory.c >>>> +++ b/drivers/base/memory.c >>>> @@ -771,10 +771,6 @@ void remove_memory_block_devices(unsigned long start, unsigned long size) >>>> struct memory_block *mem; >>>> int block_id; >>>> >>>> - if (WARN_ON_ONCE(!IS_ALIGNED(start, memory_block_size_bytes()) || >>>> - !IS_ALIGNED(size, memory_block_size_bytes()))) >>>> - return; >>>> - >>>> mutex_lock(&mem_sysfs_mutex); >>>> for (block_id = start_block_id; block_id != end_block_id; block_id++) { >>>> mem = find_memory_block_by_id(block_id, NULL); >>>> >>> >>> As I said when I introduced this, I prefer to have such duplicate checks >>> in place in case we have dependent code splattered over different files. >>> (especially mm/ vs. drivers/base). Such simple checks avoid to document >>> "start and size have to be aligned to memory blocks". >> >> Lol, I even documented it as well. So yeah, if you're going to drop this >> once, also drop the one in create_memory_block_devices(). > > TBH, I would not mind sticking with it. > What sticked out the most was that in the previous check, we BUG_on while > here we just print out a warning, so it seemed quite "inconsistent" to me. > > And I only stumbled upon this when I was testing a kernel module that > hot-removed memory in a different granularity. > > Anyway, I do not really feel strong here, I can perfectly drop this patch as I > would rather have the focus in the following-up patches, which are the important > ones IMO. Whetever you prefer, I can live with either :) (yes, separating this patch from the others makes sense) -- Thanks, David / dhildenb