From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932638AbXCAG2v (ORCPT ); Thu, 1 Mar 2007 01:28:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932702AbXCAG2v (ORCPT ); Thu, 1 Mar 2007 01:28:51 -0500 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:51819 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S932638AbXCAG2u (ORCPT ); Thu, 1 Mar 2007 01:28:50 -0500 Date: Wed, 28 Feb 2007 22:23:41 -0800 (PST) Message-Id: <20070228.222341.74751530.davem@davemloft.net> To: akpm@linux-foundation.org Cc: compudj@google.com, mbligh@google.com, linux-kernel@vger.kernel.org, ak@suse.de, paulus@samba.org, tony.luck@intel.com, hskinnemoen@atmel.com Subject: Re: Thread flags modified without set_thread_flag() (non atomically) From: David Miller In-Reply-To: <20070228220349.b42bf571.akpm@linux-foundation.org> References: <45E33EBD.6020603@google.com> <20070228220349.b42bf571.akpm@linux-foundation.org> X-Mailer: Mew version 5.1.52 on Emacs 21.4 / Mule 5.0 (SAKAKI) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Andrew Morton Date: Wed, 28 Feb 2007 22:03:49 -0800 > On Mon, 26 Feb 2007 12:10:37 -0800 Mathieu Desnoyers wrote: > > > Other examples : > > > > sparc64/kernel/ptrace.c: if > > ((task_thread_info(child)->flags & _TIF_32BIT) != 0) { > > sparc64/kernel/process.c: t->flags ^= (_TIF_ABI_PENDING | > > _TIF_32BIT); > > sparc64/kernel/process.c: t->flags &= ~_TIF_PERFCTR; > > > > sparc/kernel/process.c: current_thread_info()->flags &= > > ~_TIF_USEDFPU; > > sparc/kernel/process.c: current_thread_info()->flags &= > > ~_TIF_USEDFPU; > > sparc/kernel/process.c: current_thread_info()->flags &= > > ~_TIF_USEDFPU; > > sparc/kernel/process.c: current_thread_info()->flags &= > > ~(_TIF_USEDFPU); > > sparc/kernel/traps.c: current_thread_info()->flags |= _TIF_USEDFPU; > > sparc/kernel/traps.c: task_thread_info(fpt)->flags &= ~_TIF_USEDFPU; > > That all looks rather deliberate. > > > powerpc/kernel/process.c: t->flags ^= (_TIF_ABI_PENDING | > > _TIF_32BIT); > > > > ia64/kernel/mca.c: ti->flags = _TIF_MCA_INIT; > > > > avr32/kernel/ptrace.c: ti->flags |= _TIF_BREAKPOINT; > > No, I don't immediately see anything in the flush_old_exec() code path > which tells us that nobody else can look up this thread_info (or be holding > a ref to it) in this context. Provide the counter example, what other threads of control can modify relevant flags while a thread is exec()'ing? It's essentially frozen outside of these code paths, otherwise we wouldn't be able to make all of these modifications to the task state. I think these cases are very safe.