From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 04A6F6B0038 for ; Thu, 1 Sep 2016 21:41:30 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id c132so93471945pfg.2 for ; Thu, 01 Sep 2016 18:41:29 -0700 (PDT) Received: from szxga02-in.huawei.com (szxga02-in.huawei.com. [119.145.14.65]) by mx.google.com with ESMTPS id y32si965205otd.17.2016.09.01.18.41.27 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 01 Sep 2016 18:41:29 -0700 (PDT) Message-ID: <57C8D71F.1080803@huawei.com> Date: Fri, 2 Sep 2016 09:34:23 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [PATCH v3] memory-hotplug: fix store_mem_state() return value References: <1472743777-24266-1-git-send-email-arbab@linux.vnet.ibm.com> <20160901133717.8d753013cfbb640dd28c2783@linux-foundation.org> In-Reply-To: <20160901133717.8d753013cfbb640dd28c2783@linux-foundation.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Reza Arbab , Greg Kroah-Hartman , Vlastimil Babka , Vitaly Kuznetsov , David Rientjes , Yaowei Bai , Joonsoo Kim , Dan Williams , David Vrabel , Chen Yucong , Andrew Banman , Seth Jennings , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 2016/9/2 4:37, Andrew Morton wrote: > 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; > I think we will not execute here, it will return from device_online(), because "if (dev->offline)" is false and return 1. But the two return vaules are different if we do online-to-online. memory_subsys_online() return 0, and device_online() return 1, this is a little confusion. When device_online() return 1, online_store() return 1 and store_mem_state() return -EINVAL even without this patch, as Reza described in v2. 1. store_mem_state() called with buf="online" 2. device_online() returns 1 because device is already online 3. store_mem_state() returns 1 4. calling code interprets this as 1-byte buffer read 5. store_mem_state() called again with buf="nline" 6. store_mem_state() returns -EINVAL Thanks, Xishi Qiu > 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