From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932081AbWDYFqU (ORCPT ); Tue, 25 Apr 2006 01:46:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751395AbWDYFqT (ORCPT ); Tue, 25 Apr 2006 01:46:19 -0400 Received: from mga06.intel.com ([134.134.136.21]:42582 "EHLO orsmga101.jf.intel.com") by vger.kernel.org with ESMTP id S1751292AbWDYFqT (ORCPT ); Tue, 25 Apr 2006 01:46:19 -0400 X-IronPort-AV: i="4.04,153,1144047600"; d="scan'208"; a="27306354:sNHT16826348" X-IronPort-AV: i="4.04,153,1144047600"; d="scan'208"; a="27352984:sNHT24832626" TrustInternalSourcedMail: True X-IronPort-AV: i="4.04,153,1144047600"; d="scan'208"; a="28132177:sNHT18599469" Date: Mon, 24 Apr 2006 22:43:14 -0700 From: Keshavamurthy Anil S To: Keith Owens Cc: bibo mao , Anil S Keshavamurthy , Anderw Morton , LKML , Keith Owens , Dean Nelson , Tony Luck , Anath Mavinakayanahalli , Prasanna Panchamukhi , Dave M , Andi Kleen Subject: Re: [(take 2)patch 7/7] Notify page fault call chain Message-ID: <20060424224313.A19542@unix-os.sc.intel.com> Reply-To: Keshavamurthy Anil S References: <444C9805.4060303@linux.intel.com> <19634.1145927459@ocs3.ocs.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5.1i In-Reply-To: <19634.1145927459@ocs3.ocs.com.au>; from kaos@sgi.com on Tue, Apr 25, 2006 at 11:10:59AM +1000 X-OriginalArrivalTime: 25 Apr 2006 05:46:18.0151 (UTC) FILETIME=[92BEFB70:01C6682B] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 25, 2006 at 11:10:59AM +1000, Keith Owens wrote: > bibo mao (on Mon, 24 Apr 2006 17:19:01 +0800) wrote: > >I have some questions about page fault call chain. > >1) Can kprobe_exceptions_notify be divided into two sub-functions, one > >is for die call chain, which handles DIE_BREAK/DIE_FAULT trap, the other > >is specially for DIE_PAGE_FAULT trap. > > I asked the same question, Anil said that would/could be done in a > later set of patches, but did not want to change too much code in one > go. I don't think it is necessary to split kprobe_exception_notify(). All it is having is a simple switch case and based on the swich case it takes appropriate actions. > > >2) page_fault_notifier is conditionally registered/unregistered in this > >patch, notify_page_fault(DIE_PAGE_FAULT...) is unconditionally called in > > ia64_do_page_fault() function. I do not know whether it is possible to > >unconditionally register page_fault_notifier() call chain, but > >conditionally call notify_page_fault(DIE_PAGE_FAULT...) function. > > Only by putting extra code at the site of notify_page_fault(). That > would introduce a race against kprobes unregistering a user space > probe. The race is probably safe, but why risk it? Their is no race while we call unregister_page_fault_notifier(), as we unregister only after the last probe is removed and after synchronized_sched() is done which guarantees that all the probes have completly finished executing. > > >3) I do know whether there are other conditions like kdb/kgdb which need > >call page fault call chain when page fault happens. If only kprobe need > >handle page fault, then I think kprobe_exceptions_notify can be called > >directly in ia64_do_page_fault() function. Of course, the call chain > >method is more convenient and easy to extend for other fault causes(like > >kdb/kgdb). > > Only kprobes needs the page fault handler. > > Calling kprobe_exceptions_notify() directly would work but again it > introduces races. The register and unregister are atomic, and remember Calling kprobe_exception_notify() directly can be made to work with out any races if needed. Not sure if calling directly will have any significant performance improvement over current non-overloaded call chain notifications. -Anil