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Tue, 23 Mar 2021 21:02:31 -0700 (PDT) Date: Wed, 24 Mar 2021 09:32:29 +0530 From: Viresh Kumar To: Jie Deng Cc: linux-i2c@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, mst@redhat.com, wsa@kernel.org, jasowang@redhat.com, wsa+renesas@sang-engineering.com, andriy.shevchenko@linux.intel.com, conghui.chen@intel.com, arnd@arndb.de, kblaiech@mellanox.com, jarkko.nikula@linux.intel.com, Sergey.Semin@baikalelectronics.ru, rppt@kernel.org, loic.poulain@linaro.org, tali.perry1@gmail.com, u.kleine-koenig@pengutronix.de, bjorn.andersson@linaro.org, yu1.wang@intel.com, shuo.a.liu@intel.com, stefanha@redhat.com, pbonzini@redhat.com Subject: Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver Message-ID: <20210324040229.45gxaqfkfqjwleed@vireshk-i7> References: <226a8d5663b7bb6f5d06ede7701eedb18d1bafa1.1616493817.git.jie.deng@intel.com> <20210323090108.ygx76exdgzudeeqi@vireshk-i7> <20210323093839.n7cq7f5poebqdwit@vireshk-i7> <5a415dbe-8e3b-2731-cc52-19aeadda1a17@intel.com> <20210324035225.skkllxexjl65gs6x@vireshk-i7> <70a2d0f7-ac48-b477-8368-7ef55696bff1@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <70a2d0f7-ac48-b477-8368-7ef55696bff1@intel.com> User-Agent: NeoMutt/20180716-391-311a52 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24-03-21, 12:00, Jie Deng wrote: > > On 2021/3/24 11:52, Viresh Kumar wrote: > > On 24-03-21, 08:53, Jie Deng wrote: > > > 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 ? > > I didn't write it properly here. I wanted to say, > > > > "Can the _transfer_ actually start before virtqueue_kick() is called ?" > > > It can't start until the virtqueue_kick() is called. Call virtqueue_kick > then wait. Great, thanks for the confirmation. The code is fine then. -- viresh