From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E979AC43612 for ; Tue, 15 Jan 2019 09:43:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C1C8520657 for ; Tue, 15 Jan 2019 09:43:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728717AbfAOJnB (ORCPT ); Tue, 15 Jan 2019 04:43:01 -0500 Received: from bhuna.collabora.co.uk ([46.235.227.227]:58480 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726011AbfAOJnA (ORCPT ); Tue, 15 Jan 2019 04:43:00 -0500 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: ezequiel) with ESMTPSA id 63C4E277A6D Message-ID: Subject: Re: [PATCH RFC 2/4] media: v4l2-mem2mem: Add an optional job_done operation From: Ezequiel Garcia To: Paul Kocialkowski , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org, linux-arm-kernel@lists.infradead.org, linux-sunxi@googlegroups.com Cc: Pawel Osciak , Marek Szyprowski , Kyungmin Park , Mauro Carvalho Chehab , Maxime Ripard , Randy Li , Hans Verkuil , Tomasz Figa , Alexandre Courbot , Philipp Zabel , Laurent Pinchart , Sakari Ailus , Thomas Petazzoni Date: Tue, 15 Jan 2019 06:42:37 -0300 In-Reply-To: <20190114133839.29967-3-paul.kocialkowski@bootlin.com> References: <20190114133839.29967-1-paul.kocialkowski@bootlin.com> <20190114133839.29967-3-paul.kocialkowski@bootlin.com> Organization: Collabora Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.3-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2019-01-14 at 14:38 +0100, Paul Kocialkowski wrote: > Introduce a new optional job_done operation, which allows calling back > to the driver when a job is done. Since the job might be completed > from interrupt context where some operations are not available, having > a callback from non-atomic context allows performing these operations > upon completion of a job. This is particularly useful for releasing > access to a reference buffer, which cannot be done in atomic context. > I'm not exactly sure it makes a lot of sense to review this patch, since the approach could change. However, let me point out a few fundamental issues here. > Use the already existing v4l2_m2m_device_run_work work queue for that > and clear the M2M device current context after calling job_done in the > worker thread, so that the private data can be passed to the operation. > > Delaying the current context clearing should not be a problem since the > next call to v4l2_m2m_try_run happens right after that. > Careful here. It's misleading to think an event will happen "right after". I'd say it's either synchronously, or asynchronously. It's quite the opposite I'd say, the clearing will happen "who-knows-when the scheduler picks the thread to run" :-) Before this patch the curr_ctx was cleared in v4l2_m2m_job_finish, atomically with the ctx job flags clearing and before waking up threads waiting in v4l2_m2m_cancel_job. You are now changing this, by clearing curr_ctx in a worker. It's perfectly possible that v4l2_m2m_try_schedule will run before the worker, trying to run with the old context, which apparently would be safely refused. > Signed-off-by: Paul Kocialkowski > --- > drivers/media/v4l2-core/v4l2-mem2mem.c | 8 ++++++-- > include/media/v4l2-mem2mem.h | 4 ++++ > 2 files changed, 10 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c > index 631f4e2aa942..d5bccb0192f9 100644 > --- a/drivers/media/v4l2-core/v4l2-mem2mem.c > +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c > @@ -376,6 +376,11 @@ static void v4l2_m2m_device_run_work(struct work_struct *work) > struct v4l2_m2m_dev *m2m_dev = > container_of(work, struct v4l2_m2m_dev, job_work); > > + if (m2m_dev->m2m_ops->job_done && m2m_dev->curr_ctx) > + m2m_dev->m2m_ops->job_done(m2m_dev->curr_ctx->priv); > + > + m2m_dev->curr_ctx = NULL; > + I don't think you can access this without taking the job spinlock. > v4l2_m2m_try_run(m2m_dev); > } > Aside from this, it seems we might need this hook sooner or later. Thanks, Eze