Path: csiph.com!goblin3!goblin2!goblin.stu.neva.ru!aioe.org!bofh.it!news.nic.it!robomod From: Peter Zijlstra Newsgroups: linux.kernel Subject: Re: [RFC]: Possible race condition in kernel futex code Date: Fri, 09 Oct 2015 13:40:03 +0200 Message-ID: References: X-Original-To: Thomas Gleixner MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2012-12-30) Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 22 Organization: linux.* mail to news gateway X-Original-Cc: Hans Zuidam , Jaccon Bastiaansen , x86@kernel.org, mingo@redhat.com, "H. Peter Anvin" , "linux-kernel@vger.kernel.org" , stable@vger.kernel.org, Linus Torvalds X-Original-Date: Fri, 9 Oct 2015 13:35:52 +0200 X-Original-Message-ID: <20151009113552.GC3816@twins.programming.kicks-ass.net> X-Original-References: <4387EFE3-55AB-433B-83E1-2AFC413C7B9A@online.nl> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1243281 On Fri, Oct 09, 2015 at 11:25:09AM +0100, Thomas Gleixner wrote: > Hans, > > On Fri, 9 Oct 2015, Hans Zuidam wrote: > > On 9 okt. 2015, at 11:06, Thomas Gleixner wrote: > > > You cannot use an explicit 32bit read. We need an access which > > > handles the fault gracefully. > > > > The reason for the explicit read suggestion is to avoid the > > _builtin_constant_p() in __copy_from_user_nocheck(). The GCC manual > > says that there may be situations where it returns 0 even though the > > argument is a constant. > > That's insane at best. Right, but I bet that is for cases where constant propagation completely fails, and this is a trivial case, I have no problem relying on it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/