Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister

[Leon Romanovsky <leon@kernel.org>]

On Wed, Jul 31, 2019 at 05:00:59PM +0000, Jason Gunthorpe wrote:
> On Wed, Jul 31, 2019 at 12:22:44PM -0400, Doug Ledford wrote:
> > > diff --git a/drivers/infiniband/hw/mlx5/main.c
> > > b/drivers/infiniband/hw/mlx5/main.c
> > > index c2a5780cb394..e12a4404096b 100644
> > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > @@ -5802,13 +5802,12 @@ static void mlx5_ib_unbind_slave_port(struct
> > > mlx5_ib_dev *ibdev,
> > >  		return;
> > >  	}
> > >
> > > -	if (mpi->mdev_events.notifier_call)
> > > -		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > -	mpi->mdev_events.notifier_call = NULL;
> > > -
> > >  	mpi->ibdev = NULL;
> > >
> > >  	spin_unlock(&port->mp.mpi_lock);
> > > +	if (mpi->mdev_events.notifier_call)
> > > +		mlx5_notifier_unregister(mpi->mdev, &mpi->mdev_events);
> > > +	mpi->mdev_events.notifier_call = NULL;
> >
> > I can see where this fixes the problem at hand, but this gives the
> > appearance of creating a new race.  Doing a check/unregister/set-null
> > series outside of any locks is a red flag to someone investigating the
> > code.  You should at least make note of the fact that calling unregister
> > more than once is safe.  If you're fine with it, I can add a comment and
> > take the patch, or you can resubmit.
>
> Mucking about notifier_call like that is gross anyhow, maybe better to
> delete it entirely.

What do you propose to delete?

Doug,

I wasn't excited about that code either, but decided to do less possible harm here.

Thanks

>
> Jason