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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D796FC4332F for ; Tue, 1 Mar 2022 20:15:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237772AbiCAUQU (ORCPT ); Tue, 1 Mar 2022 15:16:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50598 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237622AbiCAUPx (ORCPT ); Tue, 1 Mar 2022 15:15:53 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1D44F793B1 for ; Tue, 1 Mar 2022 12:14:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; 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charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 01, 2022 at 07:30:32PM +0100, Sebastian Andrzej Siewior wrote: > From: Thomas Gleixner > > Use the distinction that has been made earlier between > preempt_enable_no_resched() and sched_preempt_enable_no_resched(). > sched_preempt_enable_no_resched() is used within the scheduler where an > immediate schedule() follows. preempt_enable_no_resched() is used > outside of the scheduler and an immediate schedule() invocation may not > follow for other reasons. > > The lack of an immediate schedule() invocation matters on PREEMPT_RT > where it will introduce latencies while the scheduler expects a context > switch. > > Signed-off-by: Thomas Gleixner > Signed-off-by: Sebastian Andrzej Siewior > --- > include/linux/preempt.h | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h > index b4381f255a5ca..582e43856a532 100644 > --- a/include/linux/preempt.h > +++ b/include/linux/preempt.h > @@ -210,7 +210,11 @@ do { \ > preempt_count_dec(); \ > } while (0) > > -#define preempt_enable_no_resched() sched_preempt_enable_no_resched() > +#ifdef CONFIG_PREEMPT_RT > +# define preempt_enable_no_resched() preempt_enable() > +#else > +# define preempt_enable_no_resched() sched_preempt_enable_no_resched() > +#endif Ignoring !x86 for a moment: arch/x86/mm/kmmio.c: preempt_enable_no_resched(); arch/x86/mm/kmmio.c: preempt_enable_no_resched(); include/linux/preempt.h:#define sched_preempt_enable_no_resched() \ include/linux/preempt.h:#define preempt_enable_no_resched() sched_preempt_enable_no_resched() include/linux/preempt.h:#define preempt_enable_no_resched_notrace() \ include/linux/preempt.h:#define sched_preempt_enable_no_resched() barrier() include/linux/preempt.h:#define preempt_enable_no_resched() barrier() include/linux/preempt.h:#define preempt_enable_no_resched_notrace() barrier() include/linux/preempt.h:#undef sched_preempt_enable_no_resched include/linux/preempt.h:#undef preempt_enable_no_resched include/linux/preempt.h:#undef preempt_enable_no_resched_notrace kernel/sched/core.c: preempt_enable_no_resched(); kernel/sched/core.c: preempt_enable_no_resched(); kernel/sched/core.c: sched_preempt_enable_no_resched(); kernel/sched/core.c: sched_preempt_enable_no_resched(); kernel/sched/core.c: sched_preempt_enable_no_resched(); kernel/sched/core.c: preempt_enable_no_resched_notrace(); kernel/sched/core.c: preempt_enable_no_resched_notrace(); kernel/sched/core.c: sched_preempt_enable_no_resched(); kernel/sched/core.c: sched_preempt_enable_no_resched(); kernel/signal.c: preempt_enable_no_resched(); kernel/smpboot.c: preempt_enable_no_resched(); lib/smp_processor_id.c: preempt_enable_no_resched_notrace(); Surely we can audit that... At a glance the proposed patch does more harm than good. Only the kmmio case looks obviousl fail, but then IIRC kmmio had worse problems.