Re: [PATCH] soc: mediatek: cmdq: avoid racing condition with mutex
From: CK Hu <hidden>
Date: 2019-12-30 06:44:27
Also in:
linux-devicetree, linux-mediatek, lkml
Hi, Bibby: On Thu, 2019-11-21 at 15:29 +0800, Bibby Hsieh wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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
quoted hunk ↗ jump to hunk
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; }; /**
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