From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754585AbZBIBqb (ORCPT ); Sun, 8 Feb 2009 20:46:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753615AbZBIBqX (ORCPT ); Sun, 8 Feb 2009 20:46:23 -0500 Received: from mx2.redhat.com ([66.187.237.31]:42252 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751449AbZBIBqW (ORCPT ); Sun, 8 Feb 2009 20:46:22 -0500 Date: Mon, 9 Feb 2009 02:43:55 +0100 From: Oleg Nesterov To: Roland McGrath Cc: Andrew Morton , Jerome Marchand , Denys Vlasenko , linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm 0/3] ptrace: detach wakeup fixes Message-ID: <20090209014355.GA27609@redhat.com> References: <20090208184720.GA27070@redhat.com> <20090209005405.888BFFC317@magilla.sf.frob.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090209005405.888BFFC317@magilla.sf.frob.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 02/08, Roland McGrath wrote: > > > Q: when the tracer exits we bypass ptrace_disable() and > > clear_tsk_thread_flag(TIF_SYSCALL_TRACE), is this correct? > > It's always been that way. It's obviously wrong in an abstract sense. But > for me, ptrace today is purely about compatibility with how it's behaved in > the past, however stupid that was--whenever it's been fully consistent and > predictable, userland is already saddled with coping with the stupidity. > > > Perhaps we should move this code into __ptrace_unlink? > > Locking nightmare. ptrace_disable can do stuff that may require the thread > to be stopped like other ptrace operations require (fiddle registers), > might include access_process_vm, etc. Trust me, we don't want to go there > now. OK, thanks. > (In case you were looking for reasons why I'll be soon advocating > reorganization to get ptrace entirely out of the tasklist_lock arena, this > is a fine example of the true horror that the current data structure set-up > gives us.) Heh. No, I don't need yet another reason to remove tasklist from ptrace ;) This would be obviously great. (btw, I do remember I promised the cleanup, will send a bit later). Oleg.