From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D4E9C43331 for ; Mon, 11 Nov 2019 22:38:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E669121872 for ; Mon, 11 Nov 2019 22:38:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573511911; bh=MTnAZHsrbhZ3P2DpDk2IhyzQezhY/28XsVTmndfHSJk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ykdW8VgZieTRyCdYAnylJvA3NTHIv24cGZf/CreB5n0o+XrS3UQkHT3JVFgv9b2ut BkzMg9yqQwRjCcyiJ5Fkqch/Y/0yG66hfIzlUN1s08kb1m2jTW9YFnsjeLxGxxeyby sf9XYCh6MXzbZ3AebQuM1KLeU1rUl13WDSRqxw+U= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727298AbfKKWia (ORCPT ); Mon, 11 Nov 2019 17:38:30 -0500 Received: from mail.kernel.org ([198.145.29.99]:55772 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726912AbfKKWi3 (ORCPT ); Mon, 11 Nov 2019 17:38:29 -0500 Received: from localhost (lfbn-ncy-1-150-155.w83-194.abo.wanadoo.fr [83.194.232.155]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A00E8206A3; Mon, 11 Nov 2019 22:38:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573511909; bh=MTnAZHsrbhZ3P2DpDk2IhyzQezhY/28XsVTmndfHSJk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=lMct2kYf+NtU1SSeKGfu7vJH+lus4FP6GOyRkboWV2X3sC6a6hYEvnBaDzjUm/cFG O8wPTx72oFD+CoDcM+Bn8RH1J0ao4dObawW4zfgl6LVYl/AZuIHtfkP86umsfTXR1R bv1eSQGZO9nNCe8iPPmE+Upkh4kyU4/dp8DzS0e0= Date: Mon, 11 Nov 2019 23:38:26 +0100 From: Frederic Weisbecker To: Peter Zijlstra Cc: Ingo Molnar , LKML , "Paul E . McKenney" , Thomas Gleixner Subject: Re: [RFC PATCH 4/4] irq_work: Weaken ordering in irq_work_run_list() Message-ID: <20191111223825.GA27917@lenoir> References: <20191108160858.31665-1-frederic@kernel.org> <20191108160858.31665-5-frederic@kernel.org> <20191111084313.GN4131@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191111084313.GN4131@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 11, 2019 at 09:43:13AM +0100, Peter Zijlstra wrote: > On Fri, Nov 08, 2019 at 05:08:58PM +0100, Frederic Weisbecker wrote: > > > diff --git a/kernel/irq_work.c b/kernel/irq_work.c > > index 49c53f80a13a..b709ab05cbfd 100644 > > --- a/kernel/irq_work.c > > +++ b/kernel/irq_work.c > > @@ -34,8 +34,8 @@ static bool irq_work_claim(struct irq_work *work) > > oflags = atomic_fetch_or(IRQ_WORK_CLAIMED, &work->flags); > > /* > > * If the work is already pending, no need to raise the IPI. > > + * The pairing atomic_andnot() followed by a barrier in irq_work_run() > > + * makes sure everything we did before is visible. > > */ > > if (oflags & IRQ_WORK_PENDING) > > return false; > > > @@ -151,14 +151,16 @@ static void irq_work_run_list(struct llist_head *list) > > * to claim that work don't rely on us to handle their data > > * while we are in the middle of the func. > > */ > > - flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags); > > + atomic_andnot(IRQ_WORK_PENDING, &work->flags); > > + smp_mb__after_atomic(); > > I think I'm prefering you use: > > flags = atomic_fetch_andnot_acquire(IRQ_WORK_PENDING, &work->flags); Ah good point. Preparing that. > > Also, I'm cursing at myself for the horrible comments here. Hmm, I wrote many of those, which one? :o) Thanks. > > > work->func(work); > > /* > > * Clear the BUSY bit and return to the free state if > > * no-one else claimed it meanwhile. > > */ > > - (void)atomic_cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY); > > + (void)atomic_cmpxchg(&work->flags, flags & ~IRQ_WORK_PENDING, > > + flags & ~IRQ_WORK_CLAIMED); > > } > > } > > > > -- > > 2.23.0 > >