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 3A0EF406298 for ; Mon, 15 Jun 2026 15:37:36 +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=1781537857; cv=none; b=QhVKY1I3AtK/+B7dWOXpmsuRtxRHaxTwAC9m8KNj1O0P2S90zPl9UAvEbgTzF2/HzSKZ0fv0aZUhMtvfuLJZIRJZS/uxcfYEMEEdR8XF8KqVPm7y+FoSjVOXh7ONnMarXOut4TwFeVLi28WWSlZpHKj+36HlqJ8f+K2nr0MWXnc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781537857; c=relaxed/simple; bh=BCMUhtbdZZzKDDZa4idYCJZhFcNP/10olUtbiNPkVOs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JVk2ZypYFadpu/mmLzkb0L76+t2JXN/Qgy6E85CAvAlU4LLETMLIVn/5MLJj0JGATJA4ale3+h4IS5Ua6FhquqAeJ83QqDLajnB7XcrUS17wXRoLObUwBWU+Av7yXX1xH8Cbp4Kr85xpYjBK9D5GdGfpEduX/l+aqd1wuE93/us= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HC3iCMNk; 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="HC3iCMNk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8270F1F00A3E; Mon, 15 Jun 2026 15:37:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781537856; bh=JD73ZmZn9/xEAKcgfr4nib3QjOwPG3zySjRTVt1eIWM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=HC3iCMNk4VEnr44930RZq/pgyjKDBjTh9/0NztqQTmTinIPUN8nJ5WlVBZiVtgCq2 7X5sCdUYKfDNk9BbbGgUAS0If4Nh/Dq2KYDSOqZoUQa2AZ+x6U793D9rJe3iD1Ujcx cS4nu0c13a41hqF8dCBO++Jvgj6J5lKaIbpjkpxHyRkn2u3auey/f4HAXSMrQr78aO BlucokxE9LXxBz82kkV119ao14ZERcjWjUmTeox8rM7zRd/j4ICicn72virzpk3+Zc SxbGMf0wgucgfB6D+GsCgTKD0wwrhcD9e93NFgNFO05Y+Z2RsDKyPFL7em63fdJr5c K0FLWZx+Z6uGQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Tejun Heo , Matt Fleming , Andrea Righi , Sasha Levin Subject: [PATCH 7.0.y] sched_ext: Don't warn on NULL cgrp_moving_from in scx_cgroup_move_task() Date: Mon, 15 Jun 2026 11:37:32 -0400 Message-ID: <20260615153732.2213055-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026061552-lividly-railcar-9730@gregkh> References: <2026061552-lividly-railcar-9730@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tejun Heo [ Upstream commit 02e545c4297a26dbbc41df81b831e7f605bcd306 ] A WARN fires when systemd's user manager writes "+cpu +memory +pids" to its own subtree_control while a sched_ext scheduler is loaded: WARNING: at kernel/sched/ext.c:3227 scx_cgroup_move_task+0xa8/0xb0 scx_cgroup_move_task+0xa8/0xb0 sched_move_task+0x134/0x290 cpu_cgroup_attach+0x39/0x70 cgroup_migrate_execute+0x37d/0x450 cgroup_update_dfl_csses+0x1e3/0x270 cgroup_subtree_control_write+0x3e7/0x440 scx_cgroup_can_attach() arms cgrp_moving_from only when a task's cpu cgroup changes. It can still be NULL when scx_cgroup_move_task() runs, through this sequence: Step Result --------------------------------- ---------------------------------- 1. cpu enabled on cgroup G cpu css = A 2. cpu toggled off then on for G A killed, B created (same cgroup) 3. an exiting task keeps A alive migration skips it, A now stale 4. +memory migrates G stale A vs current B pulls cpu in 5. cpu attach runs for all tasks hits a live, cpu-unchanged task 6. scx_cgroup_move_task() on it cgrp_moving_from NULL -> WARN The mismatch is that scx_cgroup_can_attach() keys on cgroup identity while migration drives the move on css identity, so a NULL cgrp_moving_from here is a legitimate css-only migration, not a missing prep. The call is already gated on cgrp_moving_from, so just drop the warning. ops.cgroup_prep_move() and ops.cgroup_move() stay paired. Fixes: 819513666966 ("sched_ext: Add cgroup support") Cc: stable@vger.kernel.org # v6.12+ Reported-by: Matt Fleming Closes: https://lore.kernel.org/all/20260601124156.2205704-1-mfleming@cloudflare.com/ Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi Signed-off-by: Sasha Levin --- kernel/sched/ext.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 38157fc58c5cc0..cfdd0d4a78ca58 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -3402,11 +3402,13 @@ void scx_cgroup_move_task(struct task_struct *p) return; /* - * @p must have ops.cgroup_prep_move() called on it and thus - * cgrp_moving_from set. + * scx_cgroup_can_attach() sets cgrp_moving_from only when the task's + * cgroup changes. Migration keys off css rather than cgroup identity, + * so it can hand an unchanged-cgroup task here with cgrp_moving_from + * NULL. Nothing to report to the BPF scheduler then, so skip it and + * keep prep_move and move paired. */ - if (SCX_HAS_OP(sch, cgroup_move) && - !WARN_ON_ONCE(!p->scx.cgrp_moving_from)) + if (SCX_HAS_OP(sch, cgroup_move) && p->scx.cgrp_moving_from) SCX_CALL_OP_TASK(sch, SCX_KF_REST, cgroup_move, task_rq(p), p, p->scx.cgrp_moving_from, tg_cgrp(task_group(p))); -- 2.53.0