linux-kernel - Re: [PATCH] mm: get_user_pages(write,force) refuse to COW in shared areas

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Date:	Fri, 25 Apr 2014 13:07:01 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Roland Dreier <roland@...nel.org>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Omar Ramirez Luna <omar.ramirez@...itl.com>,
	Inki Dae <inki.dae@...sung.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-rdma@...r.kernel.org,
	linux-media@...r.kernel.org
Subject: Re: [PATCH] mm: get_user_pages(write,force) refuse to COW in shared
 areas

On Fri, 25 Apr 2014, Oleg Nesterov wrote:
> 
> And I forgot to mention, there is another reason why I would like to
> change uprobes to follow the same convention. I still think it would
> be better to kill __replace_page() and use gup(FOLL_WRITE | FORCE)
> in uprobe_write_opcode().

Oh, please please do!  I assumed there was a good atomicity reason
for doing it that way, but if you can do it with gup() please do so.

I went off into a little rant about __replace_page() in my reply to you;
but then felt that you had approached with an honest enquiry, and didn't
deserve a rant in response, so I deleted it.

And, of course, I'm conscious that I have from start to finish withheld
my involvement from uprobes, and refused to review that __replace_page()
(beyond insisting that it not be put in a common place for sharing with
KSM, because I just couldn't guarantee it for uprobes).  I'm afraid that
it's much like HWPoison to me, a complexity (nastiness?) way beyond what
I have time to support myself.

Hugh
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