accel/habanalabs: fix bug in timestamp interrupt handling

There is a potential race between user thread seeking to re-use
a timestamp record with new interrupt id, while this record is still
in the middle of interrupt handling and it is about to be freed.
Imagine the driver set the record in_use to 0 and only then fill the
free_node information. This might lead to unpleasant scenario where
the new registration thread detects the record as free to use, and
change the cq buff address. That will cause the free_node to get
the wrong buffer address to put refcount to.

Signed-off-by: farah kassabri <fkassabri@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>

diff --git a/drivers/accel/habanalabs/common/irq.c b/drivers/accel/habanalabs/common/irq.c
index f6b6c54bc868a9b4e298618dc5c13852e69ba15d..058f270408051159f0b8fc76a2ad780e9be059c7 100644 (file)
--- a/drivers/accel/habanalabs/common/irq.c
+++ b/drivers/accel/habanalabs/common/irq.c
@@ -259,8 +259,6 @@ static int handle_registration_node(struct hl_device *hdev, struct hl_user_pendi
        dev_dbg(hdev->dev, "Irq handle: Timestamp record (%p) ts cb address (%p), interrupt_id: %u\n",
                        pend, pend->ts_reg_info.timestamp_kernel_addr, interrupt_id);
 
-       /* Mark kernel CB node as free */
-       pend->ts_reg_info.in_use = false;
        list_del(&pend->wait_list_node);
 
        /* Putting the refcount for ts_buff and cq_cb objects will be handled
@@ -270,6 +268,9 @@ static int handle_registration_node(struct hl_device *hdev, struct hl_user_pendi
        free_node->cq_cb = pend->ts_reg_info.cq_cb;
        list_add(&free_node->free_objects_node, *free_list);
 
+       /* Mark TS record as free */
+       pend->ts_reg_info.in_use = false;
+
        return 0;
 }