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Sun, 29 Dec 2019 22:44:23 -0800 Received: from mtkmbs05n2.mediatek.inc (172.21.101.140) by MTKMBS62N1.mediatek.inc (172.29.193.41) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Sun, 29 Dec 2019 22:44:37 -0800 Received: from mtkcas09.mediatek.inc (172.21.101.178) by mtkmbs05n2.mediatek.inc (172.21.101.140) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Mon, 30 Dec 2019 14:43:51 +0800 Received: from [172.21.77.4] (172.21.77.4) by mtkcas09.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Mon, 30 Dec 2019 14:44:36 +0800 Message-ID: <1577688253.17931.11.camel@mtksdaap41> Subject: Re: [PATCH] soc: mediatek: cmdq: avoid racing condition with mutex From: CK Hu To: Bibby Hsieh Date: Mon, 30 Dec 2019 14:44:13 +0800 In-Reply-To: <20191121072910.31665-1-bibby.hsieh@mediatek.com> References: <20191121072910.31665-1-bibby.hsieh@mediatek.com> X-Mailer: Evolution 3.10.4-0ubuntu2 MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191229_224431_357879_DBBEA025 X-CRM114-Status: GOOD ( 13.69 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: devicetree@vger.kernel.org, Nicolas Boichat , srv_heupstream@mediatek.com, Jassi Brar , linux-kernel@vger.kernel.org, Houlong Wei , Dennis-YC Hsieh , Rob Herring , linux-mediatek@lists.infradead.org, Matthias Brugger , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, Bibby: On Thu, 2019-11-21 at 15:29 +0800, Bibby Hsieh wrote: > If cmdq client is multi thread user, racing will occur without mutex > protection. It will make the C message queued in mailbox's queue > always need D message's triggering. > > Thread A Thread B Thread C Thread D... > ----------------------------------------------------------------------------------- > mbox_send_message() > send_data() > mbox_send_message() > *exit > mbox_send_message() > *exit > mbox_client_txdone() > tx_tick() > mbox_client_txdone() > tx_tick() > mbox_client_txdone() > tx_tick() > msg_submit() > send_data() > msg_submit() > *exit > msg_submit() > *exit > ----------------------------------------------------------------------------------- > > Signed-off-by: Bibby Hsieh > --- > drivers/soc/mediatek/mtk-cmdq-helper.c | 3 +++ > include/linux/soc/mediatek/mtk-cmdq.h | 1 + > 2 files changed, 4 insertions(+) > > diff --git a/drivers/soc/mediatek/mtk-cmdq-helper.c b/drivers/soc/mediatek/mtk-cmdq-helper.c > index 9add0fd5fa6c..9e35e0beffaa 100644 > --- a/drivers/soc/mediatek/mtk-cmdq-helper.c > +++ b/drivers/soc/mediatek/mtk-cmdq-helper.c > @@ -81,6 +81,7 @@ struct cmdq_client *cmdq_mbox_create(struct device *dev, int index, u32 timeout) > client->client.dev = dev; > client->client.tx_block = false; > client->chan = mbox_request_channel(&client->client, index); > + mutex_init(&client->mutex); > > if (IS_ERR(client->chan)) { > long err; > @@ -352,9 +353,11 @@ int cmdq_pkt_flush_async(struct cmdq_pkt *pkt, cmdq_async_flush_cb cb, > spin_unlock_irqrestore(&client->lock, flags); > } > > + mutex_lock(&client->mutex); > mbox_send_message(client->chan, pkt); > /* We can send next packet immediately, so just call txdone. */ > mbox_client_txdone(client->chan, 0); > + mutex_unlock(&client->mutex); In [1], Mediatek DRM is the first client to use cmdq and it already has its own mutex to protect this. I think helper is something help many user but now I just see Mediatek MDP [2] need this. For DRM, there are so many useless code in cmdq_pkt_flush_async(). DRM does not need the timer to check timeout. DRM could do dma_sync_single_for_cpu() in its callback and need not to create a intermediate callback to do this. I would agree this patch only when I see two or more user need this. [1] https://github.com/ckhu-mediatek/linux.git-tags/commit/4df12ed1866d1104f631e06218bd15fde512a79e [2] https://patchwork.kernel.org/patch/10945609/ Regards, CK > > return 0; > } > diff --git a/include/linux/soc/mediatek/mtk-cmdq.h b/include/linux/soc/mediatek/mtk-cmdq.h > index a74c1d5acdf3..0f9071cd1bc7 100644 > --- a/include/linux/soc/mediatek/mtk-cmdq.h > +++ b/include/linux/soc/mediatek/mtk-cmdq.h > @@ -28,6 +28,7 @@ struct cmdq_client { > struct mbox_chan *chan; > struct timer_list timer; > u32 timeout_ms; /* in unit of microsecond */ > + struct mutex mutex; > }; > > /** _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel