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Date: Tue, 21 Sep 2010 14:13:10 +0800
From: Kenneth <liguozhu@huawei.com>
Subject: Re: Problem with debugfs
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To: greg@kroah.com
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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.

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