linux-kernel - Re: [PATCH v2 3/3] mm/hwpoison: fix return value of madvise

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Date:	Tue, 27 Aug 2013 04:07:05 -0400
From:	Chen Gong <gong.chen@...ux.intel.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] mm/hwpoison: fix return value of madvise_hwpoison

On Tue, Aug 27, 2013 at 04:05:23PM +0800, Wanpeng Li wrote:
> Date: Tue, 27 Aug 2013 16:05:23 +0800
> From: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> To: Chen Gong <gong.chen@...ux.intel.com>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>, Andrew Morton
>  <akpm@...ux-foundation.org>, Andi Kleen <andi@...stfloor.org>, Fengguang
>  Wu <fengguang.wu@...el.com>, Tony Luck <tony.luck@...el.com>,
>  linux-mm@...ck.org, linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v2 3/3] mm/hwpoison: fix return value of
>  madvise_hwpoison
> User-Agent: Mutt/1.5.21 (2010-09-15)
> 
> Hi Chen,
> On Tue, Aug 27, 2013 at 03:37:01AM -0400, Chen Gong wrote:
> >On Mon, Aug 26, 2013 at 11:41:36PM -0400, Naoya Horiguchi wrote:
> >> Date: Mon, 26 Aug 2013 23:41:36 -0400
> >> From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> >> To: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> >> Cc: Andrew Morton <akpm@...ux-foundation.org>, Andi Kleen
> >>  <andi@...stfloor.org>, Fengguang Wu <fengguang.wu@...el.com>, Tony Luck
> >>  <tony.luck@...el.com>, gong.chen@...ux.intel.com, linux-mm@...ck.org,
> >>  linux-kernel@...r.kernel.org
> >> Subject: Re: [PATCH v2 3/3] mm/hwpoison: fix return value of
> >>  madvise_hwpoison
> >> User-Agent: Mutt 1.5.21 (2010-09-15)
> >> 
> >> On Tue, Aug 27, 2013 at 11:38:27AM +0800, Wanpeng Li wrote:
> >> > Hi Naoya,
> >> > On Mon, Aug 26, 2013 at 11:28:16PM -0400, Naoya Horiguchi wrote:
> >> > >On Tue, Aug 27, 2013 at 10:39:31AM +0800, Wanpeng Li wrote:
> >> > >> The return value outside for loop is always zero which means madvise_hwpoison 
> >> > >> return success, however, this is not truth for soft_offline_page w/ failure
> >> > >> return value.
> >> > >
> >> > >I don't understand what you want to do for what reason. Could you clarify
> >> > >those?
> >> > 
> >> > int ret is defined in two place in madvise_hwpoison. One is out of for
> >> > loop and its value is always zero(zero means success for madvise), the 
> >> > other one is in for loop. The soft_offline_page function maybe return 
> >> > -EBUSY and break, however, the ret out of for loop is return which means 
> >> > madvise_hwpoison success. 
> >> 
> >> Oh, I see. Thanks.
> >> 
> >I don't think such change is a good idea. The original code is obviously
> >easy to confuse people. Why not removing redundant local variable?
> >
> 
> I think the trick here is get_user_pages_fast will return the number of
> pages pinned. It is always 1 in madvise_hwpoison, the return value of
> memory_failure is ignored. Therefore we still need to reset ret to 0
> before return madvise_hwpoison.
> 
> Regards,
> Wanpeng Li
> 
It looks like the original author wrote in that way deliberately but
botching it. FWIW, I just think its harmness is more than good.

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