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[91.78.208.152]) by smtp.googlemail.com with ESMTPSA id r21sm11231014ljp.29.2020.04.06.13.54.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Apr 2020 13:54:47 -0700 (PDT) Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver To: Sowjanya Komatineni , thierry.reding@gmail.com, jonathanh@nvidia.com, frankc@nvidia.com, hverkuil@xs4all.nl, sakari.ailus@iki.fi, helen.koike@collabora.com Cc: sboyd@kernel.org, linux-media@vger.kernel.org, devicetree@vger.kernel.org, linux-clk@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <1585963507-12610-1-git-send-email-skomatineni@nvidia.com> <1585963507-12610-7-git-send-email-skomatineni@nvidia.com> <782c8c4e-f5c2-d75e-0410-757172dd3090@gmail.com> <86bbcd55-fa13-5a35-e38b-c23745eafb87@gmail.com> <2839b1ee-dedc-d0ee-e484-32729a82a6ea@nvidia.com> From: Dmitry Osipenko Message-ID: <7361d00d-9cfe-3e4a-6199-524d37d53bd0@gmail.com> Date: Mon, 6 Apr 2020 23:54:46 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <2839b1ee-dedc-d0ee-e484-32729a82a6ea@nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 06.04.2020 23:38, Sowjanya Komatineni пишет: > > On 4/6/20 1:37 PM, Dmitry Osipenko wrote: >> External email: Use caution opening links or attachments >> >> >> 06.04.2020 23:20, Sowjanya Komatineni пишет: >>> On 4/6/20 1:02 PM, Dmitry Osipenko wrote: >>>> External email: Use caution opening links or attachments >>>> >>>> >>>> 04.04.2020 04:25, Sowjanya Komatineni пишет: >>>> ... >>>>> +static int chan_capture_kthread_start(void *data) >>>>> +{ >>>>> +     struct tegra_vi_channel *chan = data; >>>>> +     struct tegra_channel_buffer *buf; >>>>> +     int err = 0; >>>>> +     int caps_inflight; >>>>> + >>>>> +     set_freezable(); >>>>> + >>>>> +     while (1) { >>>>> +             try_to_freeze(); >>>>> + >>>>> +             wait_event_interruptible(chan->start_wait, >>>>> +                                      !list_empty(&chan->capture) || >>>>> +                                      kthread_should_stop()); >>>> Is it really okay that list_empty() isn't protected with a lock? >>>> >>>> Why wait_event is "interruptible"? >>> To allow it to sleep until wakeup on thread it to avoid constant >>> checking for condition even when no buffers are ready, basically to >>> prevent blocking. >> So the "interrupt" is for getting event about kthread_should_stop(), >> correct? > also to prevent blocking and to let is sleep and wakeup based on wait > queue to evaluate condition to proceed with the task >> This looks suspicious, the comment to wait_event_interruptible() says that it will return ERESTARTSYS if signal is recieved.. Does this mean that I can send signal from userspace to wake it up? The "interruptible" part looks wrong to me.