From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762224AbYCERjl (ORCPT ); Wed, 5 Mar 2008 12:39:41 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754926AbYCERj3 (ORCPT ); Wed, 5 Mar 2008 12:39:29 -0500 Received: from extu-mxob-1.symantec.com ([216.10.194.28]:50170 "EHLO extu-mxob-1.symantec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761907AbYCERj2 (ORCPT ); Wed, 5 Mar 2008 12:39:28 -0500 Date: Wed, 5 Mar 2008 17:38:28 +0000 (GMT) From: Hugh Dickins X-X-Sender: hugh@blonde.site To: Jeremy Fitzhardinge cc: Ingo Molnar , "H. Peter Anvin" , Andi Kleen , Linux Kernel Mailing List Subject: Re: preempt bug in set_pmd_pfn? In-Reply-To: <47CECEE9.3000801@goop.org> Message-ID: References: <47CDBB87.8090906@goop.org> <20080304212821.GB8944@elte.hu> <47CDBEDC.1050302@goop.org> <20080305064814.GB28398@elte.hu> <47CECEE9.3000801@goop.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 5 Mar 2008, Jeremy Fitzhardinge wrote: > > If a thread goes from processor A -> B -> A, where A is first preempted > between a pagetable update and a tlb flush, then the second time the thread > runs on A may run with a stale tlb (if in the meantime A has either been idle > or only running kernel threads). Right, thanks, because __flush_tlb_one opts out of the full active_mm checking which goes on for userspace mms (which covers, for example, the case of preemption before dup_mmap's flush_tlb_mm). But is there actually a case where there's a problem? So far as I can see, set_pmd_pfn is there solely for discontig_32's __init remap_numa_kva; and set_pte_pfn is there solely for set_fixmap, which operates on a per-cpu area of pagetable, which would already be in bigger trouble if preemption to another cpu were possible. Hugh