From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761303AbXGPKZ5 (ORCPT ); Mon, 16 Jul 2007 06:25:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756113AbXGPKZt (ORCPT ); Mon, 16 Jul 2007 06:25:49 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:34887 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754689AbXGPKZs (ORCPT ); Mon, 16 Jul 2007 06:25:48 -0400 Date: Mon, 16 Jul 2007 15:57:38 +0530 From: Ananth N Mavinakayanahalli To: Mathieu Desnoyers Cc: Christoph Hellwig , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, prasanna@in.ibm.com, anil.s.keshavamurthy@intel.com, davem@davemloft.net Subject: Re: [patch 1/8] Kprobes - do not use kprobes mutex in arch code Message-ID: <20070716102738.GA4276@in.ibm.com> Reply-To: ananth@in.ibm.com References: <20070714012133.612727310@polymtl.ca> <20070714012411.262873138@polymtl.ca> <20070714104914.GB7358@infradead.org> <20070714192002.GK6975@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070714192002.GK6975@Krystal> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jul 14, 2007 at 03:20:02PM -0400, Mathieu Desnoyers wrote: > * Christoph Hellwig (hch@infradead.org) wrote: > > On Fri, Jul 13, 2007 at 09:21:34PM -0400, Mathieu Desnoyers wrote: > > > Remove the kprobes mutex from kprobes.h, since it does not belong there. Also > > > remove all use of this mutex in the architecture specific code, replacing it by > > > a proper mutex lock/unlock in the architecture agnostic code. > > > > This is not very nice for avr32/sparc64 which have a noop arch_remove_kprobe > > and now need to take a mutex to do nothing. Maybe you can find a nice > > way to avoid that? > > > > Except for this issue making kprobes_mutex static to kprobes.c sounds like > > a good improvement. > > > > Since only unregister_kprobe() calls arch_remove_kprobe(), and only > after having removed the struct kprobe from the kprobes list (while the > kprobes mutex is held), I wonder if there is any need to hold the > kprobes mutex at all when calling arch_remove_kprobe(). It turns out > that only get_insn_slot()/free_insn_slot() (which is in > kernel/kprobes.c, but called from arch specific code) seems to really > use protection of this mutex. Right. > Would it make sense to protect the kprobe_insn_pages list with a > new kprobe_insn_mutex, nestable in the kprobe_mutex ? Do you think it is required after your change to make kprobe_mutex static? But yes, for architectures that don't need a arch_remove_kprobe, the situation is a bit odd... a mutex to do nothing. IIRC, that was the primary reason why we made the mutex visible outside of kernel/kprobes.c Ananth