From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752817Ab1F0Rmn (ORCPT ); Mon, 27 Jun 2011 13:42:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58722 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752772Ab1F0Rmg (ORCPT ); Mon, 27 Jun 2011 13:42:36 -0400 Date: Mon, 27 Jun 2011 19:40:41 +0200 From: Oleg Nesterov To: penguin-kernel@i-love.sakura.ne.jp Cc: roland@redhat.com, linux-kernel@vger.kernel.org Subject: Re: arch_ptrace_attach() without ptrace_traceme()? Message-ID: <20110627174041.GA13983@redhat.com> References: <201106270720.p5R7Kd9E095193@www262.sakura.ne.jp> <20110627133420.GA3527@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110627133420.GA3527@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/27, Oleg Nesterov wrote: > > On 06/27, penguin-kernel@i-love.sakura.ne.jp wrote: > > > > Regarding commit f1671f6d "ptrace: fix exit_ptrace() vs ptrace_traceme() race", > > is calling arch_ptrace_attach() when ptrace_traceme() returned 0 without doing > > anything (due to PF_EXITING race) expected behavior? > > Hmm. Good point, I thinks this should be fixed. But it is not clear how we can fix this, perhaps we should ignore this problem... arch_ptrace_attach() is inherently racy when PTRACE_TRACEME is called. Please note that f1671f6d did not introduce this race, although I have to admit I didn't notice this problem when I did this patch. The race with PF_EXITING you described doesn't differ from another scenario. PF_EXITING is not set, ptrace_traceme() actually attaches the caller, but its paren exits and untraces it before it does arch_ptrace_attach(). If only I knew what arch_ptrace_attach() can do in general ;) But probably it should be paired with ptrace_disable(), and it is not called when the tracer detaches on exit anyway. So I think we can ignore this race. Oleg.