Re: [PATCH v3 06/15] NTB: ntb_transport: Avoid losing QP link-up requests

[Koichiro Den]

On Thu, Oct 15, 2026 at 12:50:29PM +0900, Koichiro Den wrote:
> On Fri, Oct 09, 2026 at 04:11:14PM -0700, Dave Jiang wrote:
> > 
> > 
> > On 9/28/26 8:25 AM, Koichiro Den wrote:
> > > ntb_netdev_open() can call ntb_transport_link_up() while the transport
> > > worker is completing setup on another CPU. Concurrent transport setup
> > > and a client link-up request can both read the other's flag as false and
> > > leave QP link work unqueued. The QP then stays down until another link
> > > event or client link-up request.
> > > 
> > > This is the store-buffering pattern described in
> > > tools/memory-model/Documentation/recipes.txt ("Store buffering").
> > > 
> > > Add a full barrier between the store and load on each side.
> > > 
> > > Fixes: fce8a7bb5b4b ("PCI-Express Non-Transparent Bridge Support")
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
> > > Link: https://lore.kernel.org/r/20260907144701.702E41F00A3A@xxxxxxxxxxxxxxx/
> > > Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
> > 
> > With Logan's comment addressed,
> > Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> > 
> > Maybe Jon can amend it on apply.
> 
> Dave, thank you as always for your review.
> 
> Jon, please let me know if you'd prefer me to resend the series with that
> amendment.

Hi Jon, Dave,

Just a gentle ping on this series.
Please let me know if you have any concerns about applying this series.

Best regards,
Koichiro Den

> 
> Best regards,
> Koichiro Den
> 
> > 
> > 
> > > ---
> > > Changes in v3:
> > >   - Drop the *_ONCE changes. client_ready is now atomic_t.
> > > 
> > > v2: https://lore.kernel.org/r/20260910040836.3792333-6-den@xxxxxxxxxxxxx/
> > > 
> > >  drivers/ntb/ntb_transport.c | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> > > 
> > > diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
> > > index 51d9e9969065..d290e5869c21 100644
> > > --- a/drivers/ntb/ntb_transport.c
> > > +++ b/drivers/ntb/ntb_transport.c
> > > @@ -1101,6 +1101,12 @@ static void ntb_transport_link_work(struct work_struct *work)
> > >  	/* Publish the link only after every QP has been set up. */
> > >  	atomic_set_release(&nt->link_is_up, true);
> > >  
> > > +	/*
> > > +	 * Prevent both sides from missing each other's flag. Pairs with
> > > +	 * the barrier in ntb_transport_link_up().
> > > +	 */
> > > +	smp_mb();
> > > +
> > >  	for (i = 0; i < nt->qp_count; i++) {
> > >  		struct ntb_transport_qp *qp = &nt->qp_vec[i];
> > >  
> > > @@ -2400,6 +2406,9 @@ void ntb_transport_link_up(struct ntb_transport_qp *qp)
> > >  
> > >  	atomic_set(&qp->client_ready, true);
> > >  
> > > +	/* Pairs with the barrier in ntb_transport_link_work(). */
> > > +	smp_mb();
> > > +
> > >  	ntb_transport_schedule_qp_link(qp, 0);
> > >  }
> > >  EXPORT_SYMBOL_GPL(ntb_transport_link_up);
> >