linux-kernel - Re: [PATCH v2] fix mlocked page counter mistmatch

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Message-Id: <20090204115047.ECB5.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Wed,  4 Feb 2009 11:51:43 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	MinChan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux mm <linux-mm@...ck.org>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v2] fix mlocked page counter mistmatch

> > Could you please teach me why this issue doesn't happend on munlockall()?
> > your scenario seems to don't depend on exit_mmap().
> 
> 
> Good question.
> It's a different issue.
> It is related to mmap_sem locking issue. 
> 
> Actually, I am about to make a patch.
> But, I can't understand that Why try_do_mlock_page should downgrade mm_sem ?
> Is it necessary ? 
> 
> In munlockall path, mmap_sem already is holding in write-mode of mmap_sem.
> so, try_to_mlock_page always fail to downgrade mmap_sem.
> It's why it looks like working well about mlocked counter. 

lastest linus tree don't have downgrade mmap_sem.
(recently it was removed)

please see it.


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