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Message-ID: <alpine.LFD.2.00.1005131256050.3711@i5.linux-foundation.org>
Date: Thu, 13 May 2010 12:59:23 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Oleg Nesterov <oleg@...hat.com>
cc: Peter Zijlstra <peterz@...radead.org>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Masami Hiramatsu <mhiramat@...hat.com>,
Randy Dunlap <rdunlap@...otime.net>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@...il.com>,
"Frank Ch. Eigler" <fche@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Roland McGrath <roland@...hat.com>, Mel Gorman <mel@....ul.ie>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v2 7/11] Uprobes Implementation
On Thu, 13 May 2010, Oleg Nesterov wrote:
>
> But I still think this doesn't actually matter, replace_page() shouldn't
> preserve the mapping, it should always install the anonymous page. I can
> be wrong, of course.
Well, if I reasd the patches right, uprobes will use "copy_to_user()" for
the self-probing case. So that would definitely just modify a shared
mapping.
Of course, arguably, who really cares? As long as it's not a security
issue (and it isn't - since the person could just have written to the
thing directly instead), I guess it doesn't much matter. But it's a bit
sad when a probing feature either
- changes a global mapping that may be executed by other non-related
processes that the prober isn't even _aware_ of.
- changes semantics by creating a non-coherent private page
so arguably it would be good to just make the rule be that you cannot
probe a shared mapping. Because whatever you do, it's always the wrong
thing.
Linus
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