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 60E1A432E94; Thu, 30 Jul 2026 14:57:27 +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=1785423448; cv=none; b=s0xkOTH47WzaZOsp+NJtw0UXNPzNUJwYJlCgUEfq3rDBhdUrLsD2UQRhwTx7GOA0rqqAxNf0P9LrcW1QFoscUHRDAaqnaXDy0kUEHRnIANdeBLEX0Ojje2Hr29mp5ttMMRDwfbXeeBZO6QCchmebEAFg60GbCGeqwIaw8q8GRYQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785423448; c=relaxed/simple; bh=IGb9ZxivJrNEvzq9RNxRKhp5+iR9niVityCY/qUVg2E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Hd9CDbFX1WHkREVJrly8ERZo9NESy/uIbGU7NdKLPOmWGilhe2AON2fImLylWlHiIXnYLEdORbAPK8mV2GKpH+nRugmYDW2bNw3uO24NYebPamnC9Ku6nTvUT85PiPoR3ObPfADWVQdJhkTCSEahsqK43BVK/Xq6dRsqUiH+C3Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=IXYNe1Z0; 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="IXYNe1Z0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 66D261F000E9; Thu, 30 Jul 2026 14:57:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1785423447; bh=XbE+fc+eSypvRMhy/EP4tbixg8YNqF5c8/vHzC/XmLQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=IXYNe1Z0VSas9PUrKnyWnIPh+3boUvnt+9PRmQ99vy+pJFc/q+qRTsFE0DvENanrE mFS0QQoPyOgKqij7P+Q/RFore4JMvg71uzNuz4qXVZ7uLUV31fleXhk8dcBaLb2UvR BfuNDxG+rtAbVKWLc8vI7IbSqI9qkheDj0gFWo6s= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Tejun Heo , Andrea Righi , Sasha Levin Subject: [PATCH 6.18 047/675] sched_ext: Dont warn on core-sched forced idle in put_prev_task_scx() Date: Thu, 30 Jul 2026 16:06:17 +0200 Message-ID: <20260730141446.119965510@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260730141445.110192266@linuxfoundation.org> References: <20260730141445.110192266@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 [ Upstream commit b7d9c359e5cf867f7eb23df3bb1c6b9e58af24da ] put_prev_task_scx() warns when a runnable task drops to a lower sched_class without SCX_OPS_ENQ_LAST, on the assumption that balance_one() would have kept it running. Core scheduling breaks that: a forced-idle SMT sibling reschedules through the core_pick fast path in pick_next_task(), which skips pick_task_scx() and thus balance_one(), so a runnable task can drop to idle with ENQ_LAST unset. Gate the warning on sched_cpu_cookie_match(): a cookie mismatch means core scheduling forced the idle, while a match (or core scheduling off) still catches a genuine missing-ENQ_LAST drop. Fixes: 7c65ae81ea86 ("sched_ext: Don't call put_prev_task_scx() before picking the next task") Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi Signed-off-by: Sasha Levin --- kernel/sched/ext.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index d399494364c0a3..83baf270888882 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -2395,9 +2395,14 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p, * sched_class, %SCX_OPS_ENQ_LAST must be set. Tell * ops.enqueue() that @p is the only one available for this cpu, * which should trigger an explicit follow-up scheduling event. + * + * Core scheduling can force this CPU idle while @p stays + * runnable. @p's cookie then won't match the core's, so skip + * the warning in that case. */ if (next && sched_class_above(&ext_sched_class, next->sched_class)) { - WARN_ON_ONCE(!(sch->ops.flags & SCX_OPS_ENQ_LAST)); + WARN_ON_ONCE(sched_cpu_cookie_match(rq, p) && + !(sch->ops.flags & SCX_OPS_ENQ_LAST)); do_enqueue_task(rq, p, SCX_ENQ_LAST, -1); } else { do_enqueue_task(rq, p, 0, -1); -- 2.53.0