On Tue, Dec 3, 2019 at 8:22 PM CK Hu [off-list ref] wrote:

Hi, Jassi:

Are mbox_send_message() and mbox_client_txdone() thread-safe? If these
two are thread-safe, this bug should be fixed in mailbox core not
client.

mbox_client_txdone should be called only when the client _knows_ the
message has been sent.
There is difference between knowing when tx is done, and assuming
tx-done because there is no way of knowing it.
Your issue arises because you immediately call mbox_client_txdone
after mbox_send_message, which may be the only way to do it but that
doesn't mean you shouldn't have to take any other precautions (like a
mutex). So I think your patch is reasonable.

Cheers!

Regards,
CK

On Thu, 2019-11-21 at 15:29 +0800, Bibby Hsieh wrote:

quoted

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);

      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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