From: Leon Romanovsky <leon@kernel.org>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: Doug Ledford <dledford@redhat.com>,
RDMA mailing list <linux-rdma@vger.kernel.org>,
Saeed Mahameed <saeedm@mellanox.com>
Subject: Re: [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister
Date: Wed, 31 Jul 2019 21:01:24 +0300 [thread overview]
Message-ID: <20190731180124.GE4832@mtr-leonro.mtl.com> (raw)
In-Reply-To: <20190731172215.GJ22677@mellanox.com>
On Wed, Jul 31, 2019 at 05:22:19PM +0000, Jason Gunthorpe wrote:
> On Wed, Jul 31, 2019 at 08:09:44PM +0300, Leon Romanovsky wrote:
> > 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?
>
> The 'mpi->mdev_events.notifier_call = NULL;' and 'if
> (mpi->mdev_events.notifier_call)'
>
> Once it leaves the lock it stops doing anything useful.
>
> If you need it, then we can't drop the lock, if you don't, it is just
> dead code, delete it.
This specific notifier_call is protected outside
of mlx5_ib_unbind_slave_port() by mlx5_ib_multiport_mutex and NULL check
is needed to ensure single call to mlx5_notifier_unregister, because
calls to mlx5_ib_unbind_slave_port() will be serialized.
Thanks
>
> Jason
next prev parent reply other threads:[~2019-07-31 18:01 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-31 8:38 [PATCH rdma-rc] RDMA/mlx5: Release locks during notifier unregister Leon Romanovsky
2019-07-31 16:22 ` Doug Ledford
2019-07-31 17:00 ` Jason Gunthorpe
2019-07-31 17:09 ` Leon Romanovsky
2019-07-31 17:22 ` Jason Gunthorpe
2019-07-31 18:01 ` Leon Romanovsky [this message]
2019-07-31 18:51 ` Doug Ledford
2019-08-01 8:22 ` Leon Romanovsky
2019-07-31 19:55 ` Jason Gunthorpe
2019-08-01 8:27 ` Leon Romanovsky
2019-08-01 12:00 ` Jason Gunthorpe
2019-08-01 12:08 ` Leon Romanovsky
2019-08-01 14:16 ` Doug Ledford
2019-08-01 15:59 ` Leon Romanovsky
2019-08-01 16:11 ` Doug Ledford
2019-08-01 16:20 ` Jason Gunthorpe
2019-08-01 16:40 ` Doug Ledford
2019-08-01 16:43 ` Jason Gunthorpe
2019-08-01 16:50 ` Doug Ledford
2019-08-01 17:31 ` Leon Romanovsky
2019-08-01 16:23 ` Leon Romanovsky
2019-08-01 16:42 ` Doug Ledford
2019-08-01 17:33 ` Leon Romanovsky
2019-08-01 20:09 ` Doug Ledford
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