linux-kernel - Re: GUP guarantees wrt to userspace mappings redesign

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Message-ID: <20160502141538.GA5961@redhat.com>
Date:	Mon, 2 May 2016 16:15:38 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Jerome Glisse <j.glisse@...il.com>,
	Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: GUP guarantees wrt to userspace mappings redesign

I am sure I missed the problem, but...

On 05/02, Kirill A. Shutemov wrote:
>
> Quick look around:
>
>  - I don't see any check page_count() around __replace_page() in uprobes,
>    so it can easily replace pinned page.

Why it should? even if it races with get_user_pages_fast()... this doesn't
differ from the case when an application writes to MAP_PRIVATE non-anonymous
region, no?

Oleg.