From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 29749 invoked by alias); 22 Mar 2006 02:37:18 -0000 Received: (qmail 29742 invoked by uid 22791); 22 Mar 2006 02:37:18 -0000 X-Spam-Status: No, hits=-2.6 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (66.187.233.31) by sourceware.org (qpsmtpd/0.31) with ESMTP; Wed, 22 Mar 2006 02:37:16 +0000 Received: from int-mx1.corp.redhat.com (int-mx1.corp.redhat.com [172.16.52.254]) by mx1.redhat.com (8.12.11.20060308/8.12.11) with ESMTP id k2M2bEil029971; Tue, 21 Mar 2006 21:37:14 -0500 Received: from pobox.toronto.redhat.com (pobox.toronto.redhat.com [172.16.14.4]) by int-mx1.corp.redhat.com (8.12.11.20060308/8.11.6) with ESMTP id k2M2bEOh002607; Tue, 21 Mar 2006 21:37:14 -0500 Received: from touchme.toronto.redhat.com (IDENT:postfix@touchme.toronto.redhat.com [172.16.14.9]) by pobox.toronto.redhat.com (8.12.8/8.12.8) with ESMTP id k2M2bDxX030241; Tue, 21 Mar 2006 21:37:13 -0500 Received: from ton.toronto.redhat.com (ton.toronto.redhat.com [172.16.14.15]) by touchme.toronto.redhat.com (Postfix) with ESMTP id 769D98003B3; Tue, 21 Mar 2006 21:37:13 -0500 (EST) Received: from ton.toronto.redhat.com (localhost.localdomain [127.0.0.1]) by ton.toronto.redhat.com (8.13.1/8.13.1) with ESMTP id k2M2bDh5019044; Tue, 21 Mar 2006 21:37:13 -0500 Received: (from fche@localhost) by ton.toronto.redhat.com (8.13.1/8.13.1/Submit) id k2M2bDq7019041; Tue, 21 Mar 2006 21:37:13 -0500 X-Authentication-Warning: ton.toronto.redhat.com: fche set sender to fche@redhat.com using -f To: Keshavamurthy Anil S Cc: systemtap@sources.redhat.com Subject: Re: thoughts about exception-handling requirements for kprobes References: <20060317135057.A18437@unix-os.sc.intel.com> <20060319172454.GA17181@in.ibm.com> <20060320103951.A10565@unix-os.sc.intel.com> <20060320185719.GA3320@in.ibm.com> <20060321144636.A31356@unix-os.sc.intel.com> From: fche@redhat.com (Frank Ch. Eigler) Date: Wed, 22 Mar 2006 02:37:00 -0000 In-Reply-To: <20060321144636.A31356@unix-os.sc.intel.com> Message-ID: User-Agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/21.3 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org X-SW-Source: 2006-q1/txt/msg00849.txt.bz2 anil.s.keshavamurthy wrote: > [...] Yes, by fixing up the exceptions(fixup_exception() call) you > are avoiding falling back to do_page_fault(), but the > copy_from_user() which generated the exception will fail and we can > not 100% reliably support copy from user from pre/post handlers even > for valid address. [...] I think that's an acceptable trade-off. It may be possible to let a systemtap user bias the system for success by arranging to page-in or even "mlock" selected processes. > Do we know how reliable is Dtrace in this respect? IIRC the documentation says that user data that is paged out at the moment of a probe will cause an error if accessed. If so, we're "tied". - FChE