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 4232FC433EF for ; Wed, 24 Nov 2021 15:43:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345182AbhKXPqI (ORCPT ); Wed, 24 Nov 2021 10:46:08 -0500 Received: from foss.arm.com ([217.140.110.172]:40206 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344869AbhKXPqH (ORCPT ); Wed, 24 Nov 2021 10:46:07 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6E87EED1; Wed, 24 Nov 2021 07:42:57 -0800 (PST) Received: from localhost.localdomain (unknown [10.57.49.75]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 3CC8B3F73B; Wed, 24 Nov 2021 07:42:56 -0800 (PST) From: Vincent Donnefort To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org Cc: linux-kernel@vger.kernel.org, mgorman@techsingularity.net, dietmar.eggemann@arm.com, valentin.schneider@arm.com, Vincent Donnefort Subject: [PATCH] sched/fair: Fix detection of per-CPU kthreads waking a task Date: Wed, 24 Nov 2021 15:42:39 +0000 Message-Id: <20211124154239.3191366-1-vincent.donnefort@arm.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org select_idle_sibling() will return prev_cpu for the case where the task is woken up by a per-CPU kthread. However, the idle task has been recently modified and is now identified by is_per_cpu_kthread(), breaking the behaviour described above. Using !is_idle_task() ensures we do not spuriously trigger that select_idle_sibling() exit path. Fixes: 00b89fe0197f ("sched: Make the idle task quack like a per-CPU kthread") Signed-off-by: Vincent Donnefort diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 945d987246c5..8bf95b0e368d 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6399,6 +6399,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) * pattern is IO completions. */ if (is_per_cpu_kthread(current) && + !is_idle_task(current) && prev == smp_processor_id() && this_rq()->nr_running <= 1) { return prev; -- 2.25.1