[PATCH] soc: mediatek: cmdq: avoid racing condition with mutex

Bibby Hsieh
2019-11-21T07:29:39Z

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 <bibby.hsieh@mediatek.com>
---
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;
};

/**
--
2.18.0