linux-kernel - Re: virt_to_page for userspace pointers

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Message-ID: <20110213220608.0c4b0cc2@lxorguk.ukuu.org.uk>
Date:	Sun, 13 Feb 2011 22:06:08 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Nikolaus Rath <Nikolaus@...h.org>
Cc:	Brice Goglin <Brice.Goglin@...-lyon.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: virt_to_page for userspace pointers

> > If you don't lock the page, you have no guarantee that it won't get
> > swapped out or migrated while you look at the physical page.
> 
> That's fine, I know that if the page is there at all then it has been
> locked by a (different) kernel driver. Is there any way to find out what
> I want?

How do you know the other driver isn't in the middle of releasing the
page ? Doing that deep in mm code without locking inversions will be fun.

Alan
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