accel/qaic: Synchronize access to DBC request queue head & tail pointer

Two threads of the same process can potential read and write parallelly to
head and tail pointers of the same DBC request queue. This could lead to a
race condition and corrupt the DBC request queue.

Fixes: ff13be8 ("accel/qaic: Add datapath")
Signed-off-by: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@quicinc.com>
Signed-off-by: Youssef Samir <youssef.abdulrahman@oss.qualcomm.com>
Reviewed-by: Jeff Hugo <jeff.hugo@oss.qualcomm.com>
Reviewed-by: Carl Vanderlip <carl.vanderlip@oss.qualcomm.com>
[jhugo: Add fixes tag]
Signed-off-by: Jeff Hugo <jeff.hugo@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20251007061837.206132-1-youssef.abdulrahman@oss.qualcomm.com

Author: Pranjal Ramajor Asha Kanojiya

drivers/accel/qaic/qaic.h

@@ -97,6 +97,8 @@ struct dma_bridge_chan {
 	 * response queue's head and tail pointer of this DBC.
 	 */
 	void __iomem		*dbc_base;
+	/* Synchronizes access to Request queue's head and tail pointer */
+	struct mutex		req_lock;
 	/* Head of list where each node is a memory handle queued in request queue */
 	struct list_head	xfer_list;
 	/* Synchronizes DBC readers during cleanup */

drivers/accel/qaic/qaic_data.c

@@ -1356,32 +1356,40 @@ static int __qaic_execute_bo_ioctl(struct drm_device *dev, void *data, struct dr
 		goto release_ch_rcu;
 	}
 
+	ret = mutex_lock_interruptible(&dbc->req_lock);
+	if (ret)
+		goto release_ch_rcu;
+
 	head = readl(dbc->dbc_base + REQHP_OFF);
 	tail = readl(dbc->dbc_base + REQTP_OFF);
 
 	if (head == U32_MAX || tail == U32_MAX) {
 		/* PCI link error */
 		ret = -ENODEV;
-		goto release_ch_rcu;
+		goto unlock_req_lock;
 	}
 
 	queue_level = head <= tail ? tail - head : dbc->nelem - (head - tail);
 
 	ret = send_bo_list_to_device(qdev, file_priv, exec, args->hdr.count, is_partial, dbc,
 				     head, &tail);
 	if (ret)
-		goto release_ch_rcu;
+		goto unlock_req_lock;
 
 	/* Finalize commit to hardware */
 	submit_ts = ktime_get_ns();
 	writel(tail, dbc->dbc_base + REQTP_OFF);
+	mutex_unlock(&dbc->req_lock);
 
 	update_profiling_data(file_priv, exec, args->hdr.count, is_partial, received_ts,
 			      submit_ts, queue_level);
 
 	if (datapath_polling)
 		schedule_work(&dbc->poll_work);
 
+unlock_req_lock:
+	if (ret)
+		mutex_unlock(&dbc->req_lock);
 release_ch_rcu:
 	srcu_read_unlock(&dbc->ch_lock, rcu_id);
 unlock_dev_srcu:

drivers/accel/qaic/qaic_drv.c

@@ -454,6 +454,9 @@ static struct qaic_device *create_qdev(struct pci_dev *pdev,
 			return NULL;
 		init_waitqueue_head(&qdev->dbc[i].dbc_release);
 		INIT_LIST_HEAD(&qdev->dbc[i].bo_lists);
+		ret = drmm_mutex_init(drm, &qdev->dbc[i].req_lock);
+		if (ret)
+			return NULL;
 	}
 
 	return qdev;