[PATCH v2 1/2] bus: mhi: host: Add spinlock to protect WP access when queueing TREs

[Qiang Yu <quic_qianyu@xxxxxxxxxxx>]

From: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>

Protect WP accesses such that multiple threads queueing buffers for
incoming data do not race and access the same WP twice. Ensure read and
write locks for the channel are not taken in succession by dropping the
read lock from parse_xfer_event() such that a callback given to client
can potentially queue buffers and acquire the write lock in that process.
Any queueing of buffers should be done without channel read lock acquired
as it can result in multiple locks and a soft lockup.

Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
Signed-off-by: Qiang Yu <quic_qianyu@xxxxxxxxxxx>
---
 drivers/bus/mhi/host/main.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
index dcf627b..13c4b89 100644
--- a/drivers/bus/mhi/host/main.c
+++ b/drivers/bus/mhi/host/main.c
@@ -642,6 +642,7 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
 			mhi_del_ring_element(mhi_cntrl, tre_ring);
 			local_rp = tre_ring->rp;
 
+			read_unlock_bh(&mhi_chan->lock);
 			/* notify client */
 			mhi_chan->xfer_cb(mhi_chan->mhi_dev, &result);
 
@@ -667,6 +668,7 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
 					kfree(buf_info->cb_buf);
 				}
 			}
+			read_lock_bh(&mhi_chan->lock);
 		}
 		break;
 	} /* CC_EOT */
@@ -1204,6 +1206,9 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 	int eot, eob, chain, bei;
 	int ret;
 
+	/* Protect accesses for reading and incrementing WP */
+	write_lock_bh(&mhi_chan->lock);
+
 	buf_ring = &mhi_chan->buf_ring;
 	tre_ring = &mhi_chan->tre_ring;
 
@@ -1221,8 +1226,10 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 
 	if (!info->pre_mapped) {
 		ret = mhi_cntrl->map_single(mhi_cntrl, buf_info);
-		if (ret)
+		if (ret) {
+			write_unlock_bh(&mhi_chan->lock);
 			return ret;
+		}
 	}
 
 	eob = !!(flags & MHI_EOB);
@@ -1239,6 +1246,8 @@ int mhi_gen_tre(struct mhi_controller *mhi_cntrl, struct mhi_chan *mhi_chan,
 	mhi_add_ring_element(mhi_cntrl, tre_ring);
 	mhi_add_ring_element(mhi_cntrl, buf_ring);
 
+	write_unlock_bh(&mhi_chan->lock);
+
 	return 0;
 }
 
-- 
2.7.4