Re: [PATCH net 1/4] NTB: ntb_transport: Recycle TX entries before client callbacks

[Dave Jiang <dave.jiang@intel.com>]

On 8/16/26 10:35 PM, Koichiro Den wrote:
> ntb_tx_copy_callback() invokes the client callback before returning the
> entry to tx_free_q. The callback may wake a stopped client queue, only
> for the next enqueue to find no local entry and return -EBUSY. The window
> is narrow, but the retry is unnecessary.
> 
> Save the callback data and length, then return the entry to tx_free_q
> before invoking the client. A completion callback then means both the
> client buffer and transport entry are ready for reuse.
> 
> Fixes: fce8a7bb5b4b ("PCI-Express Non-Transparent Bridge Support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Koichiro Den <den@valinux.co.jp>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  drivers/ntb/ntb_transport.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
> index f59f926d4bfa..e92b96f4afad 100644
> --- a/drivers/ntb/ntb_transport.c
> +++ b/drivers/ntb/ntb_transport.c
> @@ -1719,9 +1719,16 @@ static void ntb_transport_rxc_db(unsigned long data)
>  static void ntb_tx_copy_callback(void *data,
>  				 const struct dmaengine_result *res)
>  {
> +	struct ntb_payload_header __iomem *hdr;
>  	struct ntb_queue_entry *entry = data;
> -	struct ntb_transport_qp *qp = entry->qp;
> -	struct ntb_payload_header __iomem *hdr = entry->tx_hdr;
> +	struct ntb_transport_qp *qp;
> +	unsigned int len;
> +	void *cb_data;
> +
> +	qp = entry->qp;
> +	hdr = entry->tx_hdr;
> +	cb_data = entry->cb_data;
> +	len = entry->len;
>  
>  	/* we need to check DMA results if we are using DMA */
>  	if (res) {
> @@ -1768,15 +1775,13 @@ static void ntb_tx_copy_callback(void *data,
>  	 * "link down" or similar.  Since no payload is being sent in these
>  	 * cases, there is nothing to add to the completion queue.
>  	 */
> -	if (entry->len > 0) {
> -		qp->tx_bytes += entry->len;
> -
> -		if (qp->tx_handler)
> -			qp->tx_handler(qp, qp->cb_data, entry->cb_data,
> -				       entry->len);
> -	}
> +	if (len > 0)
> +		qp->tx_bytes += len;
>  
>  	ntb_list_add(&qp->ntb_tx_free_q_lock, &entry->entry, &qp->tx_free_q);
> +
> +	if (len > 0 && qp->tx_handler)
> +		qp->tx_handler(qp, qp->cb_data, cb_data, len);
>  }
>  
>  static void ntb_memcpy_tx_on_stack(struct ntb_queue_entry *entry, void __iomem *offset)