linux-kernel - Re: [RESEND PATCH v2] memory-hotplug: fix store_mem

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Date:   Wed, 31 Aug 2016 13:25:57 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Reza Arbab <arbab@...ux.vnet.ibm.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Xishi Qiu <qiuxishi@...wei.com>,
        David Vrabel <david.vrabel@...rix.com>,
        Chen Yucong <slaoub@...il.com>,
        Andrew Banman <abanman@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return
 value

On Wed, 31 Aug 2016 10:44:01 -0500 Reza Arbab <arbab@...ux.vnet.ibm.com> wrote:

> Attempting to online memory which is already online will cause this:
> 
> 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
> 
> Example:
> 
> $ cat /sys/devices/system/memory/memory0/state
> online
> $ echo online > /sys/devices/system/memory/memory0/state
> -bash: echo: write error: Invalid argument
> 
> Fix the return value of store_mem_state() so this doesn't happen.

So..  what *does* happen after the patch?  Is some sort of failure still
reported?  Or am I correct in believing that the operation will appear
to have succeeded?  If so, is that desirable?