Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver

From: Jie Deng <jie.deng@intel.com>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: mst@redhat.com, bjorn.andersson@linaro.org,
	wsa+renesas@sang-engineering.com, linux-i2c@vger.kernel.org,
	wsa@kernel.org, andriy.shevchenko@linux.intel.com,
	yu1.wang@intel.com, u.kleine-koenig@pengutronix.de,
	kblaiech@mellanox.com, virtualization@lists.linux-foundation.org,
	arnd@arndb.de, stefanha@redhat.com, tali.perry1@gmail.com,
	conghui.chen@intel.com, loic.poulain@linaro.org,
	linux-kernel@vger.kernel.org, Sergey.Semin@baikalelectronics.ru,
	jarkko.nikula@linux.intel.com, shuo.a.liu@intel.com,
	pbonzini@redhat.com, rppt@kernel.org
Subject: Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver
Date: Wed, 24 Mar 2021 08:53:34 +0800	[thread overview]
Message-ID: <5a415dbe-8e3b-2731-cc52-19aeadda1a17@intel.com> (raw)
In-Reply-To: <20210323093839.n7cq7f5poebqdwit@vireshk-i7>

On 2021/3/23 17:38, Viresh Kumar wrote:
> On 23-03-21, 14:31, Viresh Kumar wrote:
>> On 23-03-21, 22:19, Jie Deng wrote:
>>> +static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>>> +{
>>> +	struct virtio_i2c *vi = i2c_get_adapdata(adap);
>>> +	struct virtqueue *vq = vi->vq;
>>> +	struct virtio_i2c_req *reqs;
>>> +	unsigned long time_left;
>>> +	int ret, nr;
>>> +
>>> +	reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL);
>>> +	if (!reqs)
>>> +		return -ENOMEM;
>>> +
>>> +	mutex_lock(&vi->lock);
>>> +
>>> +	ret = virtio_i2c_send_reqs(vq, reqs, msgs, num);
>>> +	if (ret == 0)
>>> +		goto err_unlock_free;
>>> +
>>> +	nr = ret;
>>> +	reinit_completion(&vi->completion);
>> I think I may have found a possible bug here. This reinit_completion() must
>> happen before we call virtio_i2c_send_reqs(). It is certainly possible (surely
>> in corner cases) that virtio_i2c_msg_done() may get called right after
>> virtio_i2c_send_reqs() and before we were able to call reinit_completion(). And
>> in that case we will never see the completion happen at all.
>>
>>> +	virtqueue_kick(vq);
> I may have misread this. Can the actually start before virtqueue_kick() is
> called ?

No. It starts when wait_for_completion_timeout is called.

So it should be fine here.

>   If not, then completion may be fine where it is.
>
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