Re: Problem with debugfs

[Kenneth <liguozhu@huawei.com>]

Hi, all,

Yes, the problem is from code review, rather than in practice. I just wrote a
doc to introduce debugfs, and then I could not find a way to protect the
variable:)

I think add a comment to the header file will be good enough for this.

-- Kenneth


On Tue, Sep 21, 2010 at 02:13:10PM +0800, Kenneth wrote:
> 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
> 
>