From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 19 Jun 2008 08:38:09 -0500 From: Robin Holt Subject: Re: Can get_user_pages( ,write=1, force=1, ) result in a read-only pte and _count=2? Message-ID: <20080619133809.GC10123@sgi.com> References: <20080618164158.GC10062@sgi.com> <200806190329.30622.nickpiggin@yahoo.com.au> <200806191307.04499.nickpiggin@yahoo.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Hugh Dickins Cc: Nick Piggin , Robin Holt , Ingo Molnar , Christoph Lameter , Jack Steiner , linux-mm@kvack.org List-ID: On Thu, Jun 19, 2008 at 12:09:15PM +0100, Hugh Dickins wrote: > On Thu, 19 Jun 2008, Nick Piggin wrote: > > On Thursday 19 June 2008 05:01, Hugh Dickins wrote: > > > On Thu, 19 Jun 2008, Nick Piggin wrote: > > We're talking about swap pages, as in do_swap_page? Then AFAIKS it > > is only the mapcount that is taken into account, and get_user_pages > > will first break COW, but that should set mapcount back to 1, in > > which case the userspace access should notice that in do_swap_page > > and prevent the 2nd COW from happening. > > (I assume Robin is not forking, we do know that causes this kind > of problem, but he didn't mention any forking so I assume not.) There has been a fork long before this mapping was created. There was a hole at this location and the mapping gets established and pages populated following all ranks of the MPI job getting initialized. Thanks, Robin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org