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Date: Tue, 14 Jun 2011 16:27:10 +0200
From: Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH v4 3.0-rc2-tip 2/22]  2: uprobes: Breakground page
	replacement.
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References: <20110607125804.28590.92092.sendpatchset@localhost6.localdomain6> <20110607125835.28590.25476.sendpatchset@localhost6.localdomain6> <20110613170020.GA27137@redhat.com> <1308056477.19856.35.camel@twins>
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>, Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>, Linux-mm <linux-mm@kvack.org>, Arnaldo Carvalho de Melo <acme@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>, Hugh Dickins <hughd@google.com>, Christoph Hellwig <hch@infradead.org>, Andi Kleen <andi@firstfloor.org>, Thomas Gleixner <tglx@linutronix.de>, Jonathan Corbet <corbet@lwn.net>, Andrew Morton <akpm@linux-foundation.org>, Jim Keniston <jkenisto@linux.vnet.ibm.com>, Roland McGrath <roland@hack.frob.com>, Ananth N Mavinakayanahalli <ananth@in.ibm.com>, LKML <linux-kernel@vger.kernel.org>

On 06/14, Peter Zijlstra wrote:
>
> On Mon, 2011-06-13 at 19:00 +0200, Oleg Nesterov wrote:
> >
> > Also. This is called under down_read(mmap_sem), can't we race with
> > access_process_vm() modifying the same memory?
>
> Shouldn't matter COW and similar things are serialized using the pte
> lock.

Yes, but afaics this doesn't matter. Suppose that write_opcode() is
called when access_process_vm() does copy_to_user_page(). We can cow
the page before memcpy() completes.

Oleg.

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