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From:   Qiang Yu <quic_qianyu@quicinc.com>
To:     mani@kernel.org, quic_jhugo@quicinc.com
Cc:     mhi@lists.linux.dev, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, quic_cang@quicinc.com,
        quic_mrana@quicinc.com, Qiang Yu <quic_qianyu@quicinc.com>
Subject: [PATCH v3 2/4] bus: mhi: host: Drop chan lock before queuing buffers
Date:   Tue,  7 Nov 2023 15:16:03 +0800
Message-Id: <1699341365-47737-3-git-send-email-quic_qianyu@quicinc.com>
In-Reply-To: <1699341365-47737-1-git-send-email-quic_qianyu@quicinc.com>
References: <1699341365-47737-1-git-send-email-quic_qianyu@quicinc.com>
Precedence: bulk

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: Qiang Yu <quic_qianyu@quicinc.com>
---
 drivers/bus/mhi/host/main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/bus/mhi/host/main.c b/drivers/bus/mhi/host/main.c
index c9415b0..a236dc2 100644
--- a/drivers/bus/mhi/host/main.c
+++ b/drivers/bus/mhi/host/main.c
@@ -643,6 +643,8 @@ 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);
 
@@ -668,6 +670,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
 					kfree(buf_info->cb_buf);
 				}
 			}
+
+			read_lock_bh(&mhi_chan->lock);
 		}
 		break;
 	} /* CC_EOT */
-- 
2.7.4