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 47E1A2D9EE4; Thu, 30 Jul 2026 14:20:11 +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=1785421213; cv=none; b=m7IyYLvxqJP8qIREd5c4BTbsr+tIGWlaJDs66nmDq1dDA1ux0qhkWmEFdrV+24Or26xrNy9a5ZgGhSbR6JPbqPDRdsA8F9fI9oFXaqyIp5Jm7zX3YX+tdOhHG8hek2y7kcjcD4zEO3H4rvVqoD4zopHzclcky66MkOPpup3r+Hg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785421213; c=relaxed/simple; bh=63SzKYcpmBKDrA1b8wGxSk5F3ZHr8I4f8fdWK+yKs0A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HK3j5pF77KoGwBXK+2oQKvcJZR3B4M4Jhb60bwaW7gOeIFs5MZL2DjTlkQ5Uu0v7zF5zT89ODTBCJyUUPCaR2DkKxK+rVGJD0ID6chJZCYbdb0vBLg8UP2m39H+CuSF60thvdJrSfIsUTKEt+SobNaypDC4hSLOUtUVDLvzC9Es= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=jnlsbBU2; 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="jnlsbBU2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4E9F21F00A3A; Thu, 30 Jul 2026 14:20:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1785421211; bh=DNVcOt9DA91NQA83gnT977DyrLTiswy/cliN3ZXAtp4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=jnlsbBU2b6+7BZdgCN4QoFyYHqDfbOcfzLgKWDqNXhV7tEH7ATnURQLgRCMJyvDar /5s7UFa1kiX7i8GRPH4KfgJnMvNfpPPu7CL5dpKKlg5d1m616Ir/dYVLaBAUEsUqrz yVT2WD4LGXeptW8kM6Iu7miQzBSv4M1nY/L1ClM0= 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 7.1 028/744] sched_ext: Dont warn on core-sched forced idle in put_prev_task_scx() Date: Thu, 30 Jul 2026 16:05:01 +0200 Message-ID: <20260730141444.882893253@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260730141444.267951807@linuxfoundation.org> References: <20260730141444.267951807@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 7.1-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 0e13139a7f27b9..5f1accb092e30b 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -3097,9 +3097,14 @@ 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