From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 31E558D0039 for ; Mon, 28 Feb 2011 10:17:35 -0500 (EST) Date: Mon, 28 Feb 2011 15:15:47 +0000 From: Russell King Subject: Re: [PATCH 06/17] arm: mmu_gather rework Message-ID: <20110228151547.GC4911@flint.arm.linux.org.uk> References: <20110217162327.434629380@chello.nl> <20110217163235.106239192@chello.nl> <1298565253.2428.288.camel@twins> <1298657083.2428.2483.camel@twins> <20110225215123.GA10026@flint.arm.linux.org.uk> <1298893487.2428.10537.camel@twins> <1298902727.2428.10867.camel@twins> <20110228145750.GA4911@flint.arm.linux.org.uk> <1298905548.5226.848.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1298905548.5226.848.camel@laptop> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Andrea Arcangeli , Avi Kivity , Thomas Gleixner , Rik van Riel , Ingo Molnar , akpm@linux-foundation.org, Linus Torvalds , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Benjamin Herrenschmidt , David Miller , Hugh Dickins , Mel Gorman , Nick Piggin , Paul McKenney , Yanmin Zhang , "Luck,Tony" , PaulMundt , Chris Metcalf On Mon, Feb 28, 2011 at 04:05:48PM +0100, Peter Zijlstra wrote: > On Mon, 2011-02-28 at 14:57 +0000, Russell King wrote: > > On Mon, Feb 28, 2011 at 03:18:47PM +0100, Peter Zijlstra wrote: > > > On Mon, 2011-02-28 at 12:44 +0100, Peter Zijlstra wrote: > > > > unmap_region() > > > > tlb_gather_mmu() > > > > unmap_vmas() > > > > for (; vma; vma = vma->vm_next) > > > > unmao_page_range() > > > > tlb_start_vma() -> flush cache range > > > > > > So why is this correct? Can't we race with a concurrent access to the > > > memory region (munmap() vs other thread access race)? While > > > unmap_region() callers will have removed the vma from the tree so faults > > > will not be satisfied, TLBs might still be present and allow us to > > > access the memory and thereby reloading it in the cache. > > > > It is my understanding that code sections between tlb_gather_mmu() and > > tlb_finish_mmu() are non-preemptible - that was the case once upon a > > time when this stuff first appeared. > > It is still so, but that doesn't help with SMP. The case mentioned above > has two threads running, one doing munmap() and the other is poking at > the memory being unmapped. Luckily its a no-op on SMP capable CPUs (and actually is also a no-op on any PIPT or VIPT ARM CPU.) -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org