From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 256F4273810; Mon, 10 Nov 2025 16:08:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762790940; cv=none; b=HIRDse4I0ezGk6Ged73m+LF3N0AE9t7BzEhiVl0+7feVcAdhi401TCqyoSK3/0e6rpSM0jfoqaLyrjIlsIIl83tPSfBt02INisEXGBpdr25sML+TlSds2U+S04yXJ/WU58CoOKYOeW+vnbgMiqpblACqECnc39Ra10KAvxZezZg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762790940; c=relaxed/simple; bh=NBpmB+hnjguA3i8RznuHTjw2pYgzLf3scts8qyLJMp0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=iXr/0XN3xwADwVzsTe/BIne/Uy/bNB0ViL14P2ZMuEaWOm1PbTKcJ+8QsfJ58b7TWNYgBMbBnZa0cEeu9Rxi3tTd0nLIRnizuiVyR5GSihIgr9+Hmblv/2fxoFxsLnTamENN8OUDwTjMMrB7JiPzc42gTGxFaFrJKfuCZItcsv4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SXfklI48; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SXfklI48" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 814E9C4CEF5; Mon, 10 Nov 2025 16:08:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762790939; bh=NBpmB+hnjguA3i8RznuHTjw2pYgzLf3scts8qyLJMp0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SXfklI48xka0u1XmkPhtnSmR1XEDxmu+7Taf8hYhiJ7QRil2tCKIyZtMwR4tWraN3 iC05e2irCvyqiahWc0SzhpdYkG1SETpyhLw+q60RUZy5VV+Q7PLG+Q4rsRDAo2oyGJ KeSg0nlhWIkLLZ9fxs5dKTQuyFDmVj3JN8b95snltBjqiiMKelwj5t7VG+vnwLODC7 aQzd+VztkmpRN+DrUKNCN728sml9i9uYoJdgAutBp+4FkppZYOlzVvYqoEpR/uYMk8 hn3hp614soPecuUjiOfaL/3M9y2u5P0oPbrcqdeYlvR1OV2L/+bydl6eEOrZlEJZrt +pEnLKy21BO3A== Date: Mon, 10 Nov 2025 06:08:58 -1000 From: Tejun Heo To: Andrea Righi Cc: David Vernet , Changwoo Min , Dan Schatzberg , Emil Tsalapatis , sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org, Patrick Lu Subject: Re: [PATCH 01/13] sched_ext: Don't set ddsp_dsq_id during select_cpu in bypass mode Message-ID: References: <20251109183112.2412147-1-tj@kernel.org> <20251109183112.2412147-2-tj@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hello, On Mon, Nov 10, 2025 at 07:57:18AM +0100, Andrea Righi wrote: > On Sun, Nov 09, 2025 at 08:31:00AM -1000, Tejun Heo wrote: > > In the default CPU selection path used during bypass mode, select_task_rq_scx() > > set p->scx.ddsp_dsq_id to SCX_DSQ_LOCAL to emulate direct dispatch. However, > > do_enqueue_task() ignores ddsp_dsq_id in bypass mode and queues to the global > > DSQ, leaving ddsp_dsq_id dangling. This triggers WARN_ON_ONCE() in > > mark_direct_dispatch() if the task later gets direct dispatched. > > The patch makes sense and I was actually testing something similar to fix > https://github.com/sched-ext/scx/issues/2758. > > However, in dispatch_enqueue() we're always clearing p->scx.ddsp_dsq_id > (SCX_DSQ_INVALID), even when we're targeting the global DSQ due to bypass > mode, so in this scenario we shouldn't see a stale ddsp_dsq_id. Am I > missing something? I think you're right. The bug fix part was a wrong assumption on my part. Will update the description. Thanks. -- tejun