Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757980AbZDWRwf (ORCPT ); Thu, 23 Apr 2009 13:52:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752812AbZDWRw0 (ORCPT ); Thu, 23 Apr 2009 13:52:26 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:38105 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751782AbZDWRwZ (ORCPT ); Thu, 23 Apr 2009 13:52:25 -0400 Date: Thu, 23 Apr 2009 13:52:22 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Jeremy Fitzhardinge cc: Ingo Molnar , =?ISO-8859-15?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 In-Reply-To: <49F09C35.1080006@goop.org> Message-ID: References: <20090420222257.267399830@goodmis.org> <20090421082354.GC12512@elte.hu> <20090421094616.GA14561@elte.hu> <20090423082031.GA599@elte.hu> <49F09C35.1080006@goop.org> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2183 Lines: 53 On Thu, 23 Apr 2009, Jeremy Fitzhardinge wrote: > 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? No, I just investigated (and booted) without the raw versions (using the normal disable instead). The hooks just update variables in the task struct. I see no reason to have use it. I use to use it with ftrace, but I found that issues are caused if ftrace called something internal that used local_irq_save. Perhaps that is the issue. If something uses raw_local_irq_save then calls flush_tlb_global you might get a problem with the flags again (like we did here). But the only user of raw_* should be lockdep and irqsoff, and they should be able to deal with recursion. I don't think there should be any other user. -- Steve -- 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/