Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754604AbcJSXUJ (ORCPT ); Wed, 19 Oct 2016 19:20:09 -0400 Received: from mail-vk0-f47.google.com ([209.85.213.47]:36503 "EHLO mail-vk0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751985AbcJSXUI (ORCPT ); Wed, 19 Oct 2016 19:20:08 -0400 MIME-Version: 1.0 In-Reply-To: <1476901693-8492-2-git-send-email-mark.rutland@arm.com> References: <1476901693-8492-1-git-send-email-mark.rutland@arm.com> <1476901693-8492-2-git-send-email-mark.rutland@arm.com> From: Andy Lutomirski Date: Wed, 19 Oct 2016 16:19:46 -0700 Message-ID: Subject: Re: [PATCH 1/3] sched/core,x86: make struct thread_info arch specific again To: Mark Rutland Cc: "linux-kernel@vger.kernel.org" , linux-arch , Andrew Morton , Heiko Carstens , "H. Peter Anvin" , Kees Cook , Andrew Lutomirski , Ingo Molnar , Thomas Gleixner Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1662 Lines: 34 On Wed, Oct 19, 2016 at 11:28 AM, Mark Rutland wrote: > From: Heiko Carstens > > commit c65eacbe290b ("sched/core: Allow putting thread_info into > task_struct") made struct thread_info a generic struct with only a > single flags member if THREAD_INFO_IN_TASK_STRUCT is selected. > > This change however seems to be quite x86 centric, since at least the > generic preemption code (asm-generic/preempt.h) assumes that struct > thread_info also has a preempt_count member, which apparently was not > true for x86. > > We could add a bit more ifdefs to solve this problem too, but it seems > to be much simpler to make struct thread_info arch specific > again. This also makes the conversion to THREAD_INFO_IN_TASK_STRUCT a > bit easier for architectures that have a couple of arch specific stuff > in their thread_info definition. > > The arch specific stuff _could_ be moved to thread_struct. However > keeping them in thread_info makes it easier: accessing thread_info > members is simple, since it is at the beginning of the task_struct, > while the thread_struct is at the end. At least on s390 the offsets > needed to access members of the thread_struct (with task_struct as > base) are too large for various asm instructions. This is not a > problem when keeping these members within thread_info. Acked-by: Andy Lutomirski Ingo, there's a (somewhat weak) argument for sending this via tip/urgent: it doesn't change generated code at all, and I think it will avoid a silly depedency or possible conflict for the next merge window, since both arm64 and s390 are going to need it. --Andy