From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755892AbZDWQuS (ORCPT ); Thu, 23 Apr 2009 12:50:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752327AbZDWQuB (ORCPT ); Thu, 23 Apr 2009 12:50:01 -0400 Received: from gw.goop.org ([64.81.55.164]:60673 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751750AbZDWQuA (ORCPT ); Thu, 23 Apr 2009 12:50:00 -0400 Message-ID: <49F09C35.1080006@goop.org> Date: Thu, 23 Apr 2009 09:49:57 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Steven Rostedt CC: Ingo Molnar , =?ISO-8859-1?Q?Fr=E9d=E9ric_Weisbecker?= , LKML , Andrew Morton , Glauber de Oliveira Costa , Chris Wright , Rusty Russell , Pekka Enberg Subject: Re: [PATCH 0/2] [GIT PULL] tracing: various bug fixes References: <20090420222257.267399830@goodmis.org> <20090421082354.GC12512@elte.hu> <20090421094616.GA14561@elte.hu> <20090423082031.GA599@elte.hu> In-Reply-To: X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Steven Rostedt wrote: > Ah, this is a lockdep thing. > > The raw_local_irq_save/restore in __native_flush_tlb_global does not > update hardirqs_enabled. > > When we call into ftrace, when we cross page bounderies, we disable > interrupts using the normal local_irq_save/restore calls. > > But when we restore, it detects that interrupts are not going to be > enabled, and keeps hardirqs_enabled off. > > The printk solved the issue because it called local_irq_restore, which set > the variable back. > > I guess there's two solutions here. One, we can change the > raw_local_irq_enable/disable variants in __native_flush_tlb_global to the > non-raw type (it should protect against recursion). > > or we can try to make the ring buffer use the raw_local_irq variants too. > I tried this once before, and it did cause issues. > > Note, there's a "check_flags" in lockdep, but it is only called on > locking, it is not called when we only disable/enable interrupts. > OK, the good news is that its not a callee-save calling convention problem, which is what I feared. But it does sound pretty awkward to fix. Does __native_flush_tlb_global() have to use raw_local_irq_save/restore? J