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<492dafac-42aa-3caf-4d32-ba0e434b19c3@gmail.com> <39402a49-f39f-256c-31e7-afaa25d55664@nvidia.com> <8f01724e-95d4-e6d8-9e2d-bce4b8dd0177@nvidia.com> <5ad77b67-0dc6-3c6d-7df3-4c21c68b2b1e@gmail.com> From: Sowjanya Komatineni Message-ID: <8c8c0154-f790-f90f-e117-0d3df6823f20@nvidia.com> Date: Thu, 23 Apr 2020 19:12:07 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <5ad77b67-0dc6-3c6d-7df3-4c21c68b2b1e@gmail.com> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To DRHQMAIL107.nvidia.com (10.27.9.16) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Content-Language: en-US DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1587694212; bh=DqYjVu4skB6ZMteopOkElbiiu4dQEhuGp15nT0L9KSc=; h=X-PGP-Universal:Subject:To:CC:References:From:Message-ID:Date: User-Agent:MIME-Version:In-Reply-To:X-Originating-IP: X-ClientProxiedBy:Content-Type:Content-Transfer-Encoding: Content-Language; b=sBfUpkUAJUDZ/o29H5GkDSLlyWncUu5YW0xy869BbrEl3o7s1ALL9dMg/mlsL0VOx b5czOj8+k0PNOp8eUnnyt/a4LgCH0mrXiezgKIwhHVuhqefLp38ttahGGdz3vr2mEM 5B4JEKFg+LfDDKc/Gi2Vl8Cv5kWStW0fW8LwSpF3joU+6y/YlInqDePFco0fnsKujF 7zlQP0BCisTyjYbnd1yhJwwBUvZnFl9B6X8Cgt3gWGcg/HSl+4Ks9rOXoAPnKVnUzI d19lA5dQfkzS2jLDB/kwN8TY42eGwdGRRWdgGrKi35i48iDt8AmSRLiTe590CtJo/M YZjunCL97qgpQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/23/20 7:09 PM, Dmitry Osipenko wrote: > External email: Use caution opening links or attachments > > > 24.04.2020 04:08, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> On 4/23/20 5:51 PM, Sowjanya Komatineni wrote: >>> On 4/23/20 5:42 PM, Dmitry Osipenko wrote: >>>> External email: Use caution opening links or attachments >>>> >>>> >>>> 24.04.2020 02:50, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>>> On 4/23/20 4:25 PM, Dmitry Osipenko wrote: >>>>>> External email: Use caution opening links or attachments >>>>>> >>>>>> >>>>>> 24.04.2020 02:20, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82= : >>>>>>> On 4/23/20 4:19 PM, Sowjanya Komatineni wrote: >>>>>>>> On 4/23/20 4:16 PM, Dmitry Osipenko wrote: >>>>>>>>> External email: Use caution opening links or attachments >>>>>>>>> >>>>>>>>> >>>>>>>>> 22.04.2020 09:18, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1= =82: >>>>>>>>>> +static int chan_capture_kthread_start(void *data) >>>>>>>>>> +{ >>>>>>>>>> + struct tegra_vi_channel *chan =3D data; >>>>>>>>>> + struct tegra_channel_buffer *buf; >>>>>>>>>> + int err =3D 0; >>>>>>>>>> + >>>>>>>>>> + set_freezable(); >>>>>>>>>> + >>>>>>>>>> + while (1) { >>>>>>>>>> + try_to_freeze(); >>>>>>>>>> + >>>>>>>>>> + wait_event_interruptible(chan->start_wait, >>>>>>>>>> + !list_empty(&chan->capture) || >>>>>>>>>> + kthread_should_stop()); >>>>>>>>>> + >>>>>>>>>> + if (kthread_should_stop()) >>>>>>>>>> + break; >>>>>>>>>> + >>>>>>>>>> + /* >>>>>>>>>> + * Source is not streaming if error is non-zero. >>>>>>>>>> + * So, do not dequeue buffers on capture error. >>>>>>>>>> + */ >>>>>>>>>> + if (err) >>>>>>>>>> + continue; >>>>>>>>> This will result in an endless loop, I suppose it wasn't the >>>>>>>>> intention. >>>>>>>> no it will not. on error we report vb2_queue_error which will do >>>>>>>> streaming stop request. >>>>>>>> >>>>>>>> So thread will be stopped on streaming stop request thru kthread >>>>>>>> stop >>>>>>>> signal >>>>>>> To be clear on error it reports vb2 queue error and waits for stop >>>>>>> streaming to happen >>>>>> If thread should exit on error, then it should do it on the actual >>>>>> error. Otherwise it looks very error-prone. >>>>> When v4l2 drivers indicate fatal error through vb2_queue_error, queue >>>>> error flag is set and wakes up all processes waiting on queue along >>>>> with polling reporting EPOLLERR and also reporting error for queuing >>>>> and dequeuing buffers. Stream stop will surely happen which stops the >>>>> thread. >>>> This doesn't explain what is the point of continuing to loop instead o= f >>>> exiting immediately on error. >>> We are using 2 threads and when capture start error happens, we can >>> stop capture_start thread immediately but capture_finish thread will >>> still run for any outstanding buffers. >>> >>> So, as it makes no diff stopping both threads during stream stop which >>> will definitely happen on error and when we don't dequeue buffers >>> >> Also there will be an issue if we break on error immediately during >> stop_streaming -> kthread_stop() >> >> As stop streaming can happen any time, we do kthread_stop and in case of >> error if we stop thread and on stop streaming kthread_stop might crash >> as kthread_stop can only be called on running thread >> > This a better explanation, but still it's not good that there could be a > busy loop within the thread. > > Should be better to sleep if error is set. > > wait_event_interruptible(chan->start_wait, > (!err && !list_empty(&chan->capture)) || > kthread_should_stop()); ok, will add err to wait condition to let it sleep