From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id DF2226B01AC for ; Wed, 30 Jun 2010 15:51:34 -0400 (EDT) Date: Wed, 30 Jun 2010 12:51:21 -0700 From: Andrew Morton Subject: Re: [S+Q 01/16] [PATCH] ipc/sem.c: Bugfix for semop() not reporting successful operation Message-Id: <20100630125121.6b076f1b.akpm@linux-foundation.org> In-Reply-To: <4C2B9D43.4070504@colorfullife.com> References: <20100625212026.810557229@quilx.com> <20100625212101.622422748@quilx.com> <20100629120857.00f4b42d.akpm@linux-foundation.org> <4C2B9D43.4070504@colorfullife.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Manfred Spraul Cc: Christoph Lameter , Pekka Enberg , linux-mm@kvack.org, Nick Piggin , Matt Mackall , LKML List-ID: On Wed, 30 Jun 2010 21:38:43 +0200 Manfred Spraul wrote: > Hi Andrew, > > On 06/29/2010 09:08 PM, Andrew Morton wrote: > > On Tue, 29 Jun 2010 10:42:42 -0500 (CDT) > > Christoph Lameter wrote: > > > > > >> This is a patch from Manfred. Required to make 2.6.35-rc3 work. > >> > >> > > My current version of the patch is below. > > > > I believe that Luca has still seen problems with this patch applied so > > its current status is "stuck, awaiting developments". > > > > Is that a correct determination? > > > > I would propose that you forward a patch to Linus - either the one you > have in your tree or the v2 that I've just posted. OK, I added the incremental change: --- a/ipc/sem.c~ipc-semc-bugfix-for-semop-not-reporting-successful-operation-update +++ a/ipc/sem.c @@ -1440,7 +1440,14 @@ SYSCALL_DEFINE4(semtimedop, int, semid, if (error != -EINTR) { /* fast path: update_queue already obtained all requested - * resources */ + * resources. + * Perform a smp_mb(): User space could assume that semop() + * is a memory barrier: Without the mb(), the cpu could + * speculatively read in user space stale data that was + * overwritten by the previous owner of the semaphore. + */ + smp_mb(); + goto out_free; } _ > With stock 2.6.35-rc3, my semtimedop() stress tests produces an oops or > an invalid return value (i.e.:semtimedop() returns with "1") within a > fraction of a second. > > With either of the patches applied, my test apps show the expected behavior. OK, I'll queue it up. -- 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