linux-kernel - Re: Problem with debugfs

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Message-ID: <31aed4ad96866a97dc791186303c5719.squirrel@www.firstfloor.org>
Date:	Tue, 21 Sep 2010 09:31:58 +0200
From:	"Andi Kleen" <andi@...stfloor.org>
To:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
Cc:	"Kenneth" <liguozhu@...wei.com>, 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>, fengguang.wu@...el.com
Subject: Re: Problem with debugfs

x

>> 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.

Thanks for the report.
Copying Fengguang who wrote that code.

-Andi


>  - 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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>
>
>

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