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 34A5F44BCB8; Tue, 16 Jun 2026 16:12:51 +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=1781626372; cv=none; b=TW4ACjdx/QuKJQYdKNLWUqWhLUaSzs4XV5pQpg7cfB2qsSR7pft8QxflTyk+OhISxqeMD4LXRPxLLMp3VkV7Zwq6Oi94UxMqBC+VSSQYNEuj0d6lbMLhHrQ6NsotgQrWuU/RyrhoeUc2Yr30nJSl6DtMuel5S2gmRgUYYHUyEek= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781626372; c=relaxed/simple; bh=334CMkdeOz5Wv6CngRxIOn5va7hFczmOJEa9RMvCh/4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jVawS0sF9JgZEuZJr2S/jd2jW6KuFjd0uoaBNakRRb4E9tbauxGo7UxlXtNudF2Pb9eWO6qpqfoceedj0ZMaTf5CNBab6PvcTwItaJvPUrVAo0tW8dzZFtgvB15WHDPGmm+RKsgu1MhPODqpO73epLddIbN0ffy2Zxo3QdWjSBw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=OuXaGOKl; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="OuXaGOKl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3758D1F000E9; Tue, 16 Jun 2026 16:12:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781626371; bh=ybCEnGGIfpG5BApttri1QzaHY3Ypl1NbAoVX4H8HFnc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=OuXaGOKlBlxIC5WolSfw6HBuX5P6xYWDGTHGpKA/Cdj2Tdsfg67+qOIFDUEgZWbFv /xX1kb8fxwB16jWHUmXvjhyo2tDmWFf9UNcMWB6he1tDs3OkBuMcCAU2xNvDH0j68Y z2zU+q473i12mlDannVV3vJIxhEDmBuF9p0XmcfI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Matt Fleming , Tejun Heo , Andrea Righi , Sasha Levin Subject: [PATCH 6.18 308/325] sched_ext: Dont warn on NULL cgrp_moving_from in scx_cgroup_move_task() Date: Tue, 16 Jun 2026 20:31:44 +0530 Message-ID: <20260616145114.353125941@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145057.827196531@linuxfoundation.org> References: <20260616145057.827196531@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo commit 02e545c4297a26dbbc41df81b831e7f605bcd306 upstream. 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 [ mfleming: keep the 6.18.y SCX_KF_REST argument in the SCX_CALL_OP_TASK() call. ] Signed-off-by: Matt Fleming 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 7b750bf42698cc..d8280f87443310 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -3221,11 +3221,13 @@ 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