From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DABCF3845B3 for ; Wed, 9 Sep 2026 10:54:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788951278; cv=none; b=dgSK2gK+AN8C8JyKc3Ndu0UzifB3kgYPYeB7IAsC082y0r/umEQauuj9YTAAgVjRTGREL/aqAderuQPq8I9yM6qXVg0hYDjn25CpwOYWsbOw7Xjz7F1N6GbVKUN3VxJ4iCK/Gu+1Y0wgsNByoV9B0ZXMq8Fy4IwmKbhDkxUmd6k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788951278; c=relaxed/simple; bh=roN27aybi5JLlteX0ds4dQJ3+qMMl4CZi2532tn9GO0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=o0MFrl3BiMOz2asRvnV6Fb8MFaZ7qsucDQpI7DYsoA9fwzc1rq63/IvBx3eXrWBbicGoBUxLEE8r02LDxarLs1ze+gyXHucQTBnH5w04o6DxdrUkxQouRqD4zYtfC6Z8I3+izV1j/7NftUyC7m5Lr6K0IeNoEkad9Hh9LG1xB9w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bg/xIMOT; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bg/xIMOT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0DB551F00A3A; Wed, 9 Sep 2026 10:54:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788951273; bh=LpNv4BGSfEQ3zhCQqCfM954YRMRr69biRYUte9Y2hH8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bg/xIMOTDa8u8kgN0Wqcv5O3ruVZpqPXSm/cR24dNZKuQnQ9cfBMtlWBJCed7HsAM z3HnbYeRZR3AYsM9TtbGCpO5hNb1UvDkJyAUsY4luZ6K39yDjC1DIWx3ZSgtLQRO9Y hQ00bV2nhhqX+RgTzjY1q7/BBOWYutci1i3tMPqSbVgR6TrO3pG/Kn8T+c5cKePLEL Z48l/11qKQ0JAJbVZq0/viJboT/4LTeg8vl3JkrlkAT0fcTWXgbg9ltm92ewSYeqZK mmPe+HQOxSBOYwgUU7PX/AiMleWhuo6A0uA3u9hvl67ci0yBsc/woIgxer4OdisGxT 58gmCs1hSzKqA== From: Sasha Levin To: stable@vger.kernel.org Cc: Tejun Heo , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 6.1.y] sched/core: Make core-sched flips wait for in-flight selections Date: Wed, 9 Sep 2026 06:54:31 -0400 Message-ID: <20260909105431.1621812-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026090311-expediter-squire-a01e@gregkh> References: <2026090311-expediter-squire-a01e@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Tejun Heo [ Upstream commit f3629c63a4af3e491381780bc6c123cb498c4c40 ] Core scheduling's pick_next_task() operates on all sibling rqs under one acquisition of the shared core-wide lock. A ->pick_task() that releases the rq lock leaves every sibling __lock momentarily free, letting __sched_core_flip(false) complete mid-selection and rebind rq_lockp() under it. The selection resumes on the split locks, touching sibling state it no longer protects, and __schedule() finally releases a lock that was never taken while leaking the one that was. Count in-flight core-wide selections in the leader's rq->core_pick_in_flight and make __sched_core_flip() wait for the count to drain. The count only changes under the shared lock, which the flip holds while sampling, so no other ordering is needed. The wait can repeat while selections overlap, but the flip backs off between samples and flips are rare cookie-lifetime events. sched_core_cpu_deactivate() moves the count to the new leader - a stale copy left behind would bias it forever if that CPU later returns as its own leader. Fixes: 539f65125d20 ("sched: Add core wide task selection and scheduling") Cc: stable@vger.kernel.org # v5.14+ Signed-off-by: Tejun Heo Acked-by: Peter Zijlstra (Intel) [ Moved the counter decrement from out_set_next to out to accommodate 6.6’s cached-selection path. ] Signed-off-by: Sasha Levin --- kernel/sched/core.c | 22 ++++++++++++++++++++++ kernel/sched/sched.h | 1 + 2 files changed, 23 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index fa9008e5d8bd6..6c7759dae216f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -345,6 +345,17 @@ static void __sched_core_flip(bool enabled) sched_core_lock(cpu, &flags); + /* + * A core-wide selection may have the shared rq lock temporarily + * released by a lock-dropping ->pick_task(). Flipping would + * rebind rq_lockp() under it. Wait it out. + */ + while (cpu_rq(cpu)->core->core_pick_in_flight) { + sched_core_unlock(cpu, &flags); + cpu_relax(); + sched_core_lock(cpu, &flags); + } + for_each_cpu(t, smt_mask) cpu_rq(t)->core_enabled = enabled; @@ -5959,6 +5970,8 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) return __pick_next_task(rq, prev, rf); } + rq->core->core_pick_in_flight++; + /* * If there were no {en,de}queues since we picked (IOW, the task * pointers are all still valid), and we haven't scheduled the last @@ -6152,6 +6165,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) out_set_next: set_next_task(rq, next); out: + rq->core->core_pick_in_flight--; if (rq->core->core_forceidle_count && next == rq->idle) queue_core_balance(rq); @@ -6344,6 +6358,13 @@ static void sched_core_cpu_deactivate(unsigned int cpu) core_rq->core_forceidle_seq = rq->core_forceidle_seq; core_rq->core_forceidle_occupation = rq->core_forceidle_occupation; + /* + * A stale leftover would bias the count forever if this CPU later + * returns as its own leader. Move, don't copy. + */ + core_rq->core_pick_in_flight = rq->core_pick_in_flight; + rq->core_pick_in_flight = 0; + /* * Accounting edge for forced idle is handled in pick_next_task(). * Don't need another one here, since the hotplug thread shouldn't @@ -9834,6 +9855,7 @@ void __init sched_init(void) rq->core_forceidle_count = 0; rq->core_forceidle_occupation = 0; rq->core_forceidle_start = 0; + rq->core_pick_in_flight = 0; rq->core_cookie = 0UL; #endif diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index a6c2b8f3045ee..accff24e091e4 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1151,6 +1151,7 @@ struct rq { unsigned int core_forceidle_seq; unsigned int core_forceidle_occupation; u64 core_forceidle_start; + unsigned int core_pick_in_flight; #endif }; -- 2.53.0