From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752968AbaDCQcf (ORCPT ); Thu, 3 Apr 2014 12:32:35 -0400 Received: from e23smtp07.au.ibm.com ([202.81.31.140]:55451 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752702AbaDCQc1 (ORCPT ); Thu, 3 Apr 2014 12:32:27 -0400 Date: Thu, 3 Apr 2014 22:02:19 +0530 From: Srikar Dronamraju To: Oleg Nesterov Cc: Ingo Molnar , Ananth N Mavinakayanahalli , David Long , Denys Vlasenko , "Frank Ch. Eigler" , Jim Keniston , Jonathan Lebon , Masami Hiramatsu , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/7] uprobes: Kill UPROBE_SKIP_SSTEP and can_skip_sstep() Message-ID: <20140403163219.GA4882@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20140331194337.GA9257@redhat.com> <20140331194355.GA9275@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20140331194355.GA9275@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14040316-0260-0000-0000-000004A3A997 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > UPROBE_COPY_INSN, UPROBE_SKIP_SSTEP, and uprobe->flags must die. This > patch kills UPROBE_SKIP_SSTEP. I never understood why it was added; > not only it doesn't help, it harms. > > It can only help to avoid arch_uprobe_skip_sstep() if it was already > called before and failed. But this is ugly, if we want to know whether > we can emulate this instruction or not we should do this analysis in > arch_uprobe_analyze_insn(), not when we hit this probe for the first > time. > > And in fact this logic is simply wrong. arch_uprobe_skip_sstep() can > fail or not depending on the task/register state, if this insn can be > emulated but, say, put_user() fails we need to xol it this time, but > this doesn't mean we shouldn't try to emulate it when this or another > thread hist this bp next time. > > And this is the actual reason for this change. We need to emulate the > "call" insn, but push(return-address) can obviously fail. > > Per-arch notes: > > x86: __skip_sstep() can only emulate "rep;nop". With this > change it will be called every time and most probably > for no reason. > > This will be fixed by the next changes. We need to > change this suboptimal code anyway. > > arm: Should not be affected. It has its own "bool simulate" > flag checked in arch_uprobe_skip_sstep(). > > ppc: Looks like, it can emulate almost everything. Does it > actually needs to record the fact that emulate_step() > failed? Hopefully not. But if yes, it can add the ppc- > specific flag into arch_uprobe. > > TODO: rename arch_uprobe_skip_sstep() to arch_uprobe_emulate_insn(), > > Signed-off-by: Oleg Nesterov Acked-by: Srikar Dronamraju -- Thanks and Regards Srikar Dronamraju