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 A62BCC05027 for ; Thu, 2 Feb 2023 18:32:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232677AbjBBScw (ORCPT ); Thu, 2 Feb 2023 13:32:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34142 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232650AbjBBScf (ORCPT ); Thu, 2 Feb 2023 13:32:35 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2830D7E6DE for ; Thu, 2 Feb 2023 10:30:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675362553; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=/2CxDEOz/wKRg3fPVeBOZL5/A6pUQeGKLsIcyTY078w=; b=dzFb6Sz/l8Js9eL7OT71ft7tACdvNmXGCdEJAqhYqp+sR3+Xj3Dohrbv1yyNCjFQJ2YB3V c+dMUGkalots3EVw/RcnjbzYJcJSguCS4t7Gkk3HVD3n1yg9l+oTzpSz3WTc8yh529N0ZL JnONShKfl287lCbAXuULoZTjcTlgP0E= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-561-yacWg-_YP2WGO1gFxz4KjA-1; Thu, 02 Feb 2023 13:29:10 -0500 X-MC-Unique: yacWg-_YP2WGO1gFxz4KjA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E3C4A3810B14; Thu, 2 Feb 2023 18:29:09 +0000 (UTC) Received: from vschneid.remote.csb (unknown [10.33.36.105]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3B0DF140EBF6; Thu, 2 Feb 2023 18:29:08 +0000 (UTC) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Eder Zulian Subject: [RFC PATCH v1] sched/deadline: Add more reschedule cases to prio_changed_dl() Date: Thu, 2 Feb 2023 18:28:54 +0000 Message-Id: <20230202182854.3696665-1-vschneid@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I've been tracking down an issue on a ~5.17ish kernel where: CPUx CPUy

[idle task keeps running here until *something* accidentally sets TIF_NEED_RESCHED] On that kernel, it is quite easy to trigger using rt-tests's deadline_test [1] with the test running on isolated CPUs (this reduces the chance of something unrelated setting TIF_NEED_RESCHED on the idle tasks, making the issue even more obvious as the hung task detector chimes in). I haven't been able to reproduce this using a mainline kernel, even if I revert 2972e3050e35 ("tracing: Make trace_marker{,_raw} stream-like") which gets rid of the lock involved in the above test, *but* I cannot convince myself the issue isn't there from looking at the code. Make prio_changed_dl() issue a reschedule if the current task isn't a deadline one. While at it, ensure a reschedule is emitted when a queued-but-not-current task gets boosted with an earlier deadline that current's. [1]: https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git Signed-off-by: Valentin Schneider --- kernel/sched/deadline.c | 45 ++++++++++++++++++++++++++--------------- 1 file changed, 29 insertions(+), 16 deletions(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 0d97d54276cc8..faa382ea084c1 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2663,17 +2663,28 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p) static void prio_changed_dl(struct rq *rq, struct task_struct *p, int oldprio) { - if (task_on_rq_queued(p) || task_current(rq, p)) { -#ifdef CONFIG_SMP - /* - * This might be too much, but unfortunately - * we don't have the old deadline value, and - * we can't argue if the task is increasing - * or lowering its prio, so... - */ - if (!rq->dl.overloaded) - deadline_queue_pull_task(rq); + if (!task_on_rq_queued(p)) + return; + + /* + * We don't know if p has a earlier or later deadline, so let's blindly + * set a (maybe not needed) rescheduling point. + */ + if (!IS_ENABLED(CONFIG_SMP)) { + resched_curr(rq); + return; + } + /* + * This might be too much, but unfortunately + * we don't have the old deadline value, and + * we can't argue if the task is increasing + * or lowering its prio, so... + */ + if (!rq->dl.overloaded) + deadline_queue_pull_task(rq); + + if (task_current(rq, p)) { /* * If we now have a earlier deadline task than p, * then reschedule, provided p is still on this @@ -2681,14 +2692,16 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p, */ if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline)) resched_curr(rq); -#else + } else { /* - * Again, we don't know if p has a earlier - * or later deadline, so let's blindly set a - * (maybe not needed) rescheduling point. + * Current may not be deadline in case p was throttled but we + * have just replenished it (e.g. rt_mutex_setprio()). + * + * Otherwise, if p was given an earlier deadline, reschedule. */ - resched_curr(rq); -#endif /* CONFIG_SMP */ + if (!dl_task(rq->curr) || + dl_time_before(p->dl.deadline, rq->curr->dl.deadline)) + resched_curr(rq); } } -- 2.31.1