From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752649AbcAFORT (ORCPT ); Wed, 6 Jan 2016 09:17:19 -0500 Received: from foss.arm.com ([217.140.101.70]:35235 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752359AbcAFORQ (ORCPT ); Wed, 6 Jan 2016 09:17:16 -0500 Date: Wed, 6 Jan 2016 14:17:12 +0000 From: Catalin Marinas To: Mark Rutland Cc: cmetcalf@ezchip.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, luto@amacapital.net Subject: Re: [PATCH 2/2] arm64: factor work_pending state machine to C Message-ID: <20160106141712.GO6301@e104818-lin.cambridge.arm.com> References: <20160105172106.GA7088@leverpostej> <1452015215-29506-2-git-send-email-mark.rutland@arm.com> <20160106134313.GK563@leverpostej> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160106134313.GK563@leverpostej> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 06, 2016 at 01:43:14PM +0000, Mark Rutland wrote: > On Tue, Jan 05, 2016 at 05:33:35PM +0000, Mark Rutland wrote: > > Currently ret_fast_syscall, work_pending, and ret_to_user form an ad-hoc > > state machine that can be difficult to reason about due to duplicated > > code and a large number of branch targets. > > > > This patch factors the common logic out into the existing > > do_notify_resume function, converting the code to C in the process, > > making the code more legible. > > > > This patch tries to mirror the existing behaviour as closely as possible > > while using the usual C control flow primitives. There should be no > > functional change as a result of this patch. > > I realised there is a problem with this for kernel built with > TRACE_IRQFLAGS, as local_irq_{enable,disable}() will verify that the IRQ > state is as expected. > > In ret_fast_syscall we disable irqs behind the back of the tracer, so > when we get into do_notify_resume we'll get a splat. > > In the non-syscall cases we do not disable interrupts first, so we can't > balance things in do_notify_resume. > > We can either add a trace_hardirqs_off call to ret_fast_syscall, or we > can use raw_local_irq_{disable,enable}. The latter would match the > current behaviour (and is a nicer diff). Once the syscall path is moved > to C it would be possible to use the non-raw variants all-over. > > Catalin, are you happy with using the raw accessors in do_notify_resume, > or would you prefer using trace_hardirqs_off? I would prefer the explicit trace_hardirqs_off annotation, even though it is a few more lines. -- Catalin