From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262766AbUKRPxW (ORCPT ); Thu, 18 Nov 2004 10:53:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262527AbUKRPwT (ORCPT ); Thu, 18 Nov 2004 10:52:19 -0500 Received: from fw.osdl.org ([65.172.181.6]:16800 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S262505AbUKRPry (ORCPT ); Thu, 18 Nov 2004 10:47:54 -0500 Date: Thu, 18 Nov 2004 07:47:45 -0800 (PST) From: Linus Torvalds To: Ingo Molnar cc: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [patch, 2.6.10-rc2] fix __flush_tlb*() preemption bug on CONFIG_PREEMPT In-Reply-To: <20041118124656.GA4256@elte.hu> Message-ID: References: <20041118124656.GA4256@elte.hu> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 18 Nov 2004, Ingo Molnar wrote: > > note that reproducing this bug was only possible under PREEMPT_RT (there > it can be triggered in 30 seconds, with the right reproducer) - it needs > a really unlikely scenario which PREEMPT_RT's high concurrency does > offer but which is apparently much harder to reproduce in the vanilla > kernel. The patch fixes x86 and x64. Other architectures are most likely > safe, but they need review as well. Ok, that's a pretty race. However, I'm wondering whether this is the proper approach. After all, a lazy-tlb process should never have any reason to flush its TLB, since "its TLB" just aint there, and it ends up flushing somebody elses. So I assume that this happens only with kswapd or similar? It really might be interesting to make the "we were a lazy tlb, and we're flushing somebody else" case do a stack dump, because I _suspect_ that this really is a special thing, and maybe the right thing to do is to make it special in _that_ path. Very impressive debugging, btw. That must have been painful. Linus