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

[Koichiro Den]

On Fri, Sep 18, 2026 at 06:10:39PM -0700, Joe Damato wrote:
> 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@xxxxxxxxxxxxxxx
> > Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
> > Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260904052134.2970111-1-den%40valinux.co.jp?part=3
> > Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> > ---
> > 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

There are no concurrent writers to entry->flags here, so I think the plain load
on the right hand side is fine.

Best regards,
Koichiro