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 6D8B6C43219 for ; Mon, 24 Jan 2022 23:58:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2367119AbiAXXyM (ORCPT ); Mon, 24 Jan 2022 18:54:12 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1837907AbiAXWpe (ORCPT ); Mon, 24 Jan 2022 17:45:34 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B248C0550CC; Mon, 24 Jan 2022 13:05:56 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id DC1196142E; Mon, 24 Jan 2022 21:05:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AC90EC340E5; Mon, 24 Jan 2022 21:05:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643058355; bh=bRSguhJPl84harqENFcTRVmow9GIgHPy1csFS3mmJgc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GPDib1kgn+XJ4rW5nCXjJl/UMc3HpysAQX6W7sRGXJyYZsEKq3dpRE5pqCXEMbqZ6 i9lbS0uwXA2lhH/ihvZLP4wppRFA4bom0ZGqXsfJBTpbk6ACMJNzDzRGYapdRGu3/G YneZH12yIp5T0N2xnNxhptydTjaVNZnTfIagzfVw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vincent Donnefort , "Peter Zijlstra (Intel)" , Vincent Guittot , Valentin Schneider , Sasha Levin Subject: [PATCH 5.16 0230/1039] sched/fair: Fix detection of per-CPU kthreads waking a task Date: Mon, 24 Jan 2022 19:33:39 +0100 Message-Id: <20220124184133.054095952@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124184125.121143506@linuxfoundation.org> References: <20220124184125.121143506@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vincent Donnefort [ Upstream commit 8b4e74ccb582797f6f0b0a50372ebd9fd2372a27 ] select_idle_sibling() has a special case for tasks woken up by a per-CPU kthread, where the selected CPU is the previous one. However, the current condition for this exit path is incomplete. A task can wake up from an interrupt context (e.g. hrtimer), while a per-CPU kthread is running. A such scenario would spuriously trigger the special case described above. Also, a recent change made the idle task like a regular per-CPU kthread, hence making that situation more likely to happen (is_per_cpu_kthread(swapper) being true now). Checking for task context makes sure select_idle_sibling() will not interpret a wake up from any other context as a wake up by a per-CPU kthread. Fixes: 52262ee567ad ("sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression") Signed-off-by: Vincent Donnefort Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Vincent Guittot Reviewed-by: Valentin Schneider Link: https://lore.kernel.org/r/20211201143450.479472-1-vincent.donnefort@arm.com Signed-off-by: Sasha Levin --- kernel/sched/fair.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6e476f6d94351..97d89516fbea2 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6398,6 +6398,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) * pattern is IO completions. */ if (is_per_cpu_kthread(current) && + in_task() && prev == smp_processor_id() && this_rq()->nr_running <= 1) { return prev; -- 2.34.1