linux-kernel - Re: Question about PRIVATE

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Message-ID: <28c262360903262132n1f3d3c1ctbbafa1bc22dc3ddd@mail.gmail.com>
Date:	Fri, 27 Mar 2009 13:32:05 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Eric Dumazet <dada1@...mosbay.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: Question about PRIVATE_FUTEX

Hmm, It seems even shared futex, too.

After calling get_user_pages_fast, get_futex_key calls unlock, put_page, too.
Then futex_wait  calls get_futex_value_locked.
Wouldn't kernel reclaim the page between get_fuex_key and
get_futex_value_locked ?

How do we make sure this race condition ?


On Fri, Mar 27, 2009 at 11:12 AM, Minchan Kim <minchan.kim@...il.com> wrote:
> Hi, Peter and Eric.
>
> I am not expert about futex.
> I am sorry if this is dumb question.
>
> If we use private futex, get_futex_key don't call get_user_pages_fast
> which pins page at page table.
> Then, get_futex_value_locked calls __cpy_from_user_inatomic with
> pagefault_disable.
>
> Who make sure the user page is mapped at app's page table ?
>
> --
> Kinds regards,
> Minchan Kim
>



-- 
Kinds regards,
Minchan Kim
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