From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx107.postini.com [74.125.245.107]) by kanga.kvack.org (Postfix) with SMTP id EA5466B0072 for ; Fri, 26 Oct 2012 10:14:36 -0400 (EDT) Received: by mail-ee0-f41.google.com with SMTP id c4so1302379eek.14 for ; Fri, 26 Oct 2012 07:14:35 -0700 (PDT) Date: Fri, 26 Oct 2012 16:14:30 +0200 From: Ingo Molnar Subject: Re: [PATCH 26/31] sched, numa, mm: Add fault driven placement and migration policy Message-ID: <20121026141430.GA12158@gmail.com> References: <20121025121617.617683848@chello.nl> <20121025124834.467791319@chello.nl> <20121026071532.GC8141@gmail.com> <20121026135024.GA11640@gmail.com> <1351260672.16863.81.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1351260672.16863.81.camel@twins> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Linus Torvalds , Rik van Riel , Andrea Arcangeli , Mel Gorman , Johannes Weiner , Thomas Gleixner , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org * Peter Zijlstra wrote: > On Fri, 2012-10-26 at 15:50 +0200, Ingo Molnar wrote: > > > > Oh, just found the reason: > > > > the ptep_modify_prot_start()/modify()/commit() sequence is > > SMP-unsafe - it has to be done under the mmap_sem > > write-locked. > > > > It is safe against *hardware* updates to the PTE, but not > > safe against itself. > > Shouldn't the pte_lock serialize all that still? All sites > that modify PTE contents should hold the pte_lock (and do > afaict). Hm, indeed. Is there no code under down_read() (in the page fault path) that modifies the pte via just pure atomics? Thanks, Ingo -- 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