netdev - Re: [PATCH rdma-next 1/2] RDMA/mlx5: Get upper device only if device is lagged

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Message-ID: <ZONo++BgYux82Wjo@nvidia.com>
Date: Mon, 21 Aug 2023 10:39:07 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: Mark Bloch <mbloch@...dia.com>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, linux-rdma@...r.kernel.org,
	Mark Zhang <markzhang@...dia.com>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>, Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH rdma-next 1/2] RDMA/mlx5: Get upper device only if device
 is lagged

On Sun, Aug 20, 2023 at 12:59:26PM +0300, Leon Romanovsky wrote:
> On Fri, Aug 18, 2023 at 01:42:30PM -0300, Jason Gunthorpe wrote:
> > On Fri, Aug 18, 2023 at 01:33:35PM -0300, Jason Gunthorpe wrote:
> > > On Wed, Aug 16, 2023 at 09:52:23AM +0300, Leon Romanovsky wrote:
> > > > From: Mark Bloch <mbloch@...dia.com>
> > > > 
> > > > If the RDMA device isn't in LAG mode there is no need
> > > > to try to get the upper device.
> > > > 
> > > > Signed-off-by: Mark Bloch <mbloch@...dia.com>
> > > > Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> > > > ---
> > > >  drivers/infiniband/hw/mlx5/main.c | 22 +++++++++++++++-------
> > > >  1 file changed, 15 insertions(+), 7 deletions(-)
> > > > 
> > > > diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
> > > > index f0b394ed7452..215d7b0add8f 100644
> > > > --- a/drivers/infiniband/hw/mlx5/main.c
> > > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > > @@ -195,12 +195,18 @@ static int mlx5_netdev_event(struct notifier_block *this,
> > > >  	case NETDEV_CHANGE:
> > > >  	case NETDEV_UP:
> > > >  	case NETDEV_DOWN: {
> > > > -		struct net_device *lag_ndev = mlx5_lag_get_roce_netdev(mdev);
> > > >  		struct net_device *upper = NULL;
> > > >  
> > > > -		if (lag_ndev) {
> > > > -			upper = netdev_master_upper_dev_get(lag_ndev);
> > > > -			dev_put(lag_ndev);
> > > > +		if (ibdev->lag_active) {
> > > 
> > > Needs locking to read lag_active
> > 
> > Specifically the use of the bitfield looks messed up.. If lag_active
> > and some others were set only during probe it could be OK.
> 
> All fields except ib_active are static and set during probe.
> 
> > 
> > But mixing other stuff that is being written concurrently is not OK to
> > do like this. (eg ib_active via a mlx5 notifier)
> 
> What you are looking is the following change, did I get you right?
> 
> diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> index 9d0c56b59ed2..ee73113717b2 100644
> --- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
> +++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> @@ -1094,7 +1094,7 @@ struct mlx5_ib_dev {
>         /* serialize update of capability mask
>          */
>         struct mutex                    cap_mask_mutex;
> -       u8                              ib_active:1;
> +       bool                            ib_active;
>         u8                              is_rep:1;
>         u8                              lag_active:1;
>         u8                              wc_support:1;

That helps, but it still needs some kind of concurrency management for
ib_active

Jason