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 7DB0C45BD6F; Tue, 16 Jun 2026 16:36:58 +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=1781627819; cv=none; b=aRP2rNKEkvT2VC1V1IqeTN6eVJKfbnj91cwoMf/EcIP7mCU0m4c9qE1W2xBy7y1DAa2nB3tUKfYlewk3gAXM24t2xRVOHbxxfUWjMxuclcd6wUittZvcJxqJ0F61BnbULgucHqTXcu/NPy0nBoMSOVQHQuhoGP2ernWnK4Izs8E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781627819; c=relaxed/simple; bh=zsMPzBeimjk0LRBxZcdKTuyFy1Z2KCrVNmjDHUag5/4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=fNTpBxV/MEfDv+cgjdp53QkvcpOAK7AbXQg3+TsKbXwhuQ5esMZiVsHIrdyljnOb2LR897/1GFT3vE8v4QaK6rZhdtG+3uGDXwdo1QLGrf+AUu5RhHJ4zVLGjpe85g1D55W+lxfD//GBZJmO+QNf+01m66Q6nEZv357pEmo56EU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ecH+hYPA; 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="ecH+hYPA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E0B61F000E9; Tue, 16 Jun 2026 16:36:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781627818; bh=0IwPab4tN4Z/R7Qsehp6lLoJfbjFyLy77z0olP+aJ9c=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ecH+hYPAW7gWaHHBzLtvbercwg68VPyiGZ0IgAXvQpp7z+TP3zVP3PGRnju5EJru3 VtuAU3j3Qs3hkCplkA7y/s6E9Z91RDdcdNurUtmWrEpECSxsXxvjCmvPC5lkJPBykh H/GwHd0aBHESx5Kw03j7B82LoKzTeAdSL/FmykoI= 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 6.12 233/261] sched_ext: Dont warn on NULL cgrp_moving_from in scx_cgroup_move_task() Date: Tue, 16 Jun 2026 20:31:11 +0530 Message-ID: <20260616145055.846440038@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145044.869532709@linuxfoundation.org> References: <20260616145044.869532709@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ 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 Signed-off-by: Greg Kroah-Hartman --- kernel/sched/ext.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -4069,10 +4069,13 @@ void scx_cgroup_move_task(struct task_st 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(cgroup_move) && !WARN_ON_ONCE(!p->scx.cgrp_moving_from)) + if (SCX_HAS_OP(cgroup_move) && p->scx.cgrp_moving_from) SCX_CALL_OP_TASK(SCX_KF_UNLOCKED, cgroup_move, p, p->scx.cgrp_moving_from, tg_cgrp(task_group(p))); p->scx.cgrp_moving_from = NULL;