Re: [PATCH v3] accel/qaic: Handle DBC deactivation if the owner went away

[Lizhi Hou <lizhi.hou@amd.com>]

Reviewed-by: Lizhi Hou <lizhi.hou@amd.com>

On 2/5/26 04:34, Youssef Samir wrote:
> 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>
> ---
> Changes in V3:
> - Remove unnecessary list_empty() check
> - Link to V2: https://lore.kernel.org/all/20251224143009.2769836-1-youssef.abdulrahman@oss.qualcomm.com
>
> Changes in V2:
> - Add missing closing bracket in resp_worker()
> - Link to V1: https://lore.kernel.org/all/20251223153151.2232297-1-youssef.abdulrahman@oss.qualcomm.com
> ---
>   drivers/accel/qaic/qaic_control.c | 47 +++++++++++++++++++++++++++++--
>   1 file changed, 45 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/accel/qaic/qaic_control.c b/drivers/accel/qaic/qaic_control.c
> index 428d8f65bff3..3842e59291b9 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 (ret == -ERESTARTSYS)
> +		ret = 0;
>   	if (!ret && !elem.buf)
>   		ret = -ETIMEDOUT;
>   	else if (ret > 0 && !elem.buf)
> @@ -1418,9 +1421,49 @@ 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);
> +	}
>   
>   	kfree(resp);
>   }