From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f199.google.com (mail-qt0-f199.google.com [209.85.216.199]) by kanga.kvack.org (Postfix) with ESMTP id 5D3396B0038 for ; Thu, 1 Sep 2016 16:37:20 -0400 (EDT) Received: by mail-qt0-f199.google.com with SMTP id 101so208143472qtb.0 for ; Thu, 01 Sep 2016 13:37:20 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id u129si1851707pfu.78.2016.09.01.13.37.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Sep 2016 13:37:19 -0700 (PDT) Date: Thu, 1 Sep 2016 13:37:17 -0700 From: Andrew Morton Subject: Re: [PATCH v3] memory-hotplug: fix store_mem_state() return value Message-Id: <20160901133717.8d753013cfbb640dd28c2783@linux-foundation.org> In-Reply-To: <1472743777-24266-1-git-send-email-arbab@linux.vnet.ibm.com> References: <1472743777-24266-1-git-send-email-arbab@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Reza Arbab Cc: Greg Kroah-Hartman , Vlastimil Babka , Vitaly Kuznetsov , David Rientjes , Yaowei Bai , Joonsoo Kim , Dan Williams , Xishi Qiu , David Vrabel , Chen Yucong , Andrew Banman , Seth Jennings , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, 1 Sep 2016 10:29:37 -0500 Reza Arbab wrote: > If store_mem_state() is called to online memory which is already online, > it will return 1, the value it got from device_online(). > > This is wrong because store_mem_state() is a device_attribute .store > function. Thus a non-negative return value represents input bytes read. > > Set the return value to -EINVAL in this case. > I actually made the mistake of reading this code. What the heck are the return value semantics of bus_type.online? Sometimes 0, sometimes 1 and apparently sometimes -Efoo values. What are these things trying to tell the caller and why is "1" ever useful and why doesn't anyone document anything. grr. And now I don't understand this patch. Because: static int memory_subsys_online(struct device *dev) { struct memory_block *mem = to_memory_block(dev); int ret; if (mem->state == MEM_ONLINE) return 0; Doesn't that "return 0" contradict the changelog? Also, is store_mem_state() the correct place to fix this? Instead, should memory_block_change_state() detect an attempt to online already-online memory and itself return -EINVAL, and permit that to be propagated back? Well, that depends on the bus_type.online rules which appear to be undocumented. What is the bus implementation supposed to do when a request is made to online an already-online device? -- 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