linux-kernel - Re: Problem with debugfs

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Message-Id: <20100921162316.3C03.A69D9226@jp.fujitsu.com>
Date:	Tue, 21 Sep 2010 16:23:56 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Kenneth <liguozhu@...wei.com>
Cc:	kosaki.motohiro@...fujitsu.com, greg@...ah.com,
	linux-kernel@...r.kernel.org,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andi Kleen <andi@...stfloor.org>, linux-mm <linux-mm@...ck.org>
Subject: Re: Problem with debugfs

> Hello, Mr. Greg,
> 
> I'm sorry I had not checked the git before sending my last mail.
> 
> For the problem I mention, consider this scenarios:
> 
> 1. mm/hwpoinson-inject.c create a debugfs file with
>    debugfs_create_u64("corrupt-filter-flags-mask", ...,
>    &hwpoison_filter_flags_mask)
> 2. hwpoison_filter_flags_mask is supposed to be protected by filp->priv->mutex
>    of this file when it is accessed from user space.
> 3. but when it is accessed from mm/memory-failure.c:hwpoison_filter_flags,
>    there is no way for the function to protect the operation (so it simply
>    ignore it). This may create a competition problem.
> 
> It should be a problem.
> 
> I'm sorry from my poor English skill.

I think your english is very clear :)
Let's cc hwpoison folks.


 - kosaki 


> 
> Best Regards
> Kenneth Lee
> 
> On Tue, Sep 21, 2010 at 10:21:12AM +0800, kenny wrote:
> > Hi, there,
> > 
> > I do not know who is the maintainer for debugfs now. But I think there is
> > problem with its API: It uses filp->priv->mutex to protect the read/write (to
> > the file) for the value of its attribute, but the mutex is not exported to the
> > API user.  Therefore, there is no way to protect its value when you directly
> > use the value in your module.
> > 
> > Is my understanding correct?
> > 
> > Thanks
> > 
> > 
> > Best Regards
> > Kenneth Lee
> 
> 
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