Re: [PATCH net-next v4 03/10] NTB: ntb_transport: Order RX entry completion

[Joe Damato <joe@dama.to>]

On Mon, Sep 14, 2026 at 05:48:31PM +0900, Koichiro Den wrote:
> RX entries are added to rx_post_q before their fields are filled in.
> The overflow path sets DONE without a write barrier, and
> ntb_complete_rxc() has no read barrier after checking DONE. A concurrent
> completion can therefore consume stale entry fields.
> 
> Publish DONE with release ordering and check it with acquire ordering in
> ntb_complete_rxc(). Use the same publication rule in the copy callback.
> 
> Fixes: da2e5ae56164 ("NTB: Fix ntb_transport out-of-order RX update")
> Cc: stable@vger.kernel.org
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260904052134.2970111-1-den%40valinux.co.jp?part=3
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
> ---
> Changes in v4:
>   - New patch (Sashiko)
> 
>  drivers/ntb/ntb_transport.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
> index 3f497a62673f..b69e8ac8047d 100644
> --- a/drivers/ntb/ntb_transport.c
> +++ b/drivers/ntb/ntb_transport.c

[...]

> -	entry->flags |= DESC_DONE_FLAG;
> +	/* Pair with the acquire load in ntb_complete_rxc(). */
> +	smp_store_release(&entry->flags, entry->flags | DESC_DONE_FLAG);
                                          ^^^^^^^^^^^


>  
>  	ntb_complete_rxc(entry->qp);
>  }
> @@ -1664,7 +1666,8 @@ static int ntb_process_rxc(struct ntb_transport_qp *qp)
>  		qp->rx_err_oflow++;
>  
>  		entry->len = -EIO;
> -		entry->flags |= DESC_DONE_FLAG;
> +		/* Pair with the acquire load in ntb_complete_rxc(). */
> +		smp_store_release(&entry->flags, entry->flags | DESC_DONE_FLAG);
                                                 ^^^^^^^^^^^^

are these two smp_store_release lines right? i am asking because it looks like
they do a load ? i honestly have no idea if there is a race here but it looks
sus to me