patch "bus: mhi: host: Drop chan lock before queuing buffers" added to char-misc-next

This is a note to let you know that I've just added the patch titled

bus: mhi: host: Drop chan lock before queuing buffers

to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-next branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release during the merge window.

If you have any questions about this process, please let me know.

From 01bd694ac2f682fb8017e16148b928482bc8fa4b Mon Sep 17 00:00:00 2001
From: Qiang Yu <[email protected]>
Date: Mon, 11 Dec 2023 14:42:52 +0800
Subject: bus: mhi: host: Drop chan lock before queuing buffers

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.

---
 drivers/bus/mhi/host/main.c | 4 ++++
 1 file changed, 4 insertions(+)

index ad7807e4b523..abb561db9ae1 100644
@@ -644,6 +644,8 @@ 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);
 

@@ -669,6 +671,8 @@ static int parse_xfer_event(struct mhi_controller *mhi_cntrl,
 					kfree(buf_info->cb_buf);
 				}
 			}
+
+			read_lock_bh(&mhi_chan->lock);
 		}
 		break;
 	} /* CC_EOT */

2.43.0