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* [PATCH] accel/qaic: Handle DBC deactivation if the owner went away
@ 2025-12-23 15:31 Youssef Samir
  2025-12-24  5:43 ` kernel test robot
  2025-12-24 10:11 ` kernel test robot
  0 siblings, 2 replies; 3+ messages in thread
From: Youssef Samir @ 2025-12-23 15:31 UTC (permalink / raw)
  To: jeff.hugo, carl.vanderlip, troy.hanson, zachary.mckevitt
  Cc: ogabbay, lizhi.hou, karol.wachowski, linux-arm-msm, dri-devel

When a DBC is released, the device sends a QAIC_TRANS_DEACTIVATE_FROM_DEV
transaction to the host over the QAIC_CONTROL MHI channel. QAIC handles
this by calling decode_deactivate() to release the resources allocated for
that DBC. Since that handling is done in the qaic_manage_ioctl() context,
if the user goes away before receiving and handling the deactivation, the
host will be out-of-sync with the DBCs available for use, and the DBC
resources will not be freed unless the device is removed. If another user
loads and requests to activate a network, then the device assigns the same
DBC to that network, QAIC will "indefinitely" wait for dbc->in_use = false,
leading the user process to hang.

As a solution to this, handle QAIC_TRANS_DEACTIVATE_FROM_DEV transactions
that are received after the user has gone away.

Fixes: 129776ac2e38 ("accel/qaic: Add control path")
Signed-off-by: Youssef Samir <youssef.abdulrahman@oss.qualcomm.com>
---
 drivers/accel/qaic/qaic_control.c | 46 +++++++++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/drivers/accel/qaic/qaic_control.c b/drivers/accel/qaic/qaic_control.c
index 428d8f65bff3..16bdae028935 100644
--- a/drivers/accel/qaic/qaic_control.c
+++ b/drivers/accel/qaic/qaic_control.c
@@ -913,7 +913,7 @@ static int decode_deactivate(struct qaic_device *qdev, void *trans, u32 *msg_len
 		 */
 		return -ENODEV;
 
-	if (status) {
+	if (usr && status) {
 		/*
 		 * Releasing resources failed on the device side, which puts
 		 * us in a bind since they may still be in use, so enable the
@@ -1108,6 +1108,9 @@ static void *msg_xfer(struct qaic_device *qdev, struct wrapper_list *wrappers, u
 	mutex_lock(&qdev->cntl_mutex);
 	if (!list_empty(&elem.list))
 		list_del(&elem.list);
+	/* resp_worker() processed the response but the wait was interrupted */
+	else if (list_empty(&elem.list) && ret == -ERESTARTSYS)
+		ret = 0;
 	if (!ret && !elem.buf)
 		ret = -ETIMEDOUT;
 	else if (ret > 0 && !elem.buf)
@@ -1418,7 +1421,46 @@ static void resp_worker(struct work_struct *work)
 	}
 	mutex_unlock(&qdev->cntl_mutex);
 
-	if (!found)
+	if (!found) {
+		/*
+		 * The user might have gone away at this point without waiting
+		 * for QAIC_TRANS_DEACTIVATE_FROM_DEV transaction coming from
+		 * the device. If this is not handled correctly, the host will
+		 * not know that the DBC[n] has been freed on the device.
+		 * Due to this failure in synchronization between the device and
+		 * the host, if another user requests to activate a network, and
+		 * the device assigns DBC[n] again, save_dbc_buf() will hang,
+		 * waiting for dbc[n]->in_use to be set to false, which will not
+		 * happen unless the qaic_dev_reset_clean_local_state() gets
+		 * called by resetting the device (or re-inserting the module).
+		 *
+		 * As a solution, we look for QAIC_TRANS_DEACTIVATE_FROM_DEV
+		 * transactions in the message before disposing of it, then
+		 * handle releasing the DBC resources.
+		 *
+		 * Since the user has gone away, if the device could not
+		 * deactivate the network (status != 0), there is no way to
+		 * enable and reassign the DBC to the user. We can put trust in
+		 * the device that it will release all the active DBCs in
+		 * response to the QAIC_TRANS_TERMINATE_TO_DEV transaction,
+		 * otherwise, the user can issue an soc_reset to the device.
+		 */
+		u32 msg_count = le32_to_cpu(msg->hdr.count);
+		u32 msg_len = le32_to_cpu(msg->hdr.len);
+		u32 len = 0;
+		int j;
+
+		for (j = 0; j < msg_count && len < msg_len; ++j) {
+			struct wire_trans_hdr *trans_hdr;
+
+			trans_hdr = (struct wire_trans_hdr *)(msg->data + len);
+			if (le32_to_cpu(trans_hdr->type) == QAIC_TRANS_DEACTIVATE_FROM_DEV) {
+				if (decode_deactivate(qdev, trans_hdr, &len, NULL))
+					len += le32_to_cpu(trans_hdr->len);
+			} else {
+				len += le32_to_cpu(trans_hdr->len);
+			}
+		}
 		/* request must have timed out, drop packet */
 		kfree(msg);
 
-- 
2.43.0


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2025-12-23 15:31 [PATCH] accel/qaic: Handle DBC deactivation if the owner went away Youssef Samir
2025-12-24  5:43 ` kernel test robot
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