netdev - RE: [EXTERNAL] Re: [Patch rdma-next] RDMA/mana_ib: handle net event for pointing to the current netdev

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Message-ID:
 <SA6PR21MB42318A621DA625465D88780FCECB2@SA6PR21MB4231.namprd21.prod.outlook.com>
Date: Wed, 5 Mar 2025 00:00:58 +0000
From: Long Li <longli@...rosoft.com>
To: Jason Gunthorpe <jgg@...pe.ca>
CC: Ratheesh Kannoth <rkannoth@...vell.com>, "longli@...uxonhyperv.com"
	<longli@...uxonhyperv.com>, Leon Romanovsky <leon@...nel.org>, Konstantin
 Taranov <kotaranov@...rosoft.com>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, "linux-rdma@...r.kernel.org"
	<linux-rdma@...r.kernel.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-hyperv@...r.kernel.org"
	<linux-hyperv@...r.kernel.org>
Subject: RE: [EXTERNAL] Re: [Patch rdma-next] RDMA/mana_ib: handle net event
 for pointing to the current netdev

> Subject: Re: [EXTERNAL] Re: [Patch rdma-next] RDMA/mana_ib: handle net
> event for pointing to the current netdev
> 
> On Tue, Mar 04, 2025 at 06:26:03PM +0000, Long Li wrote:
> > > On 2025-03-01 at 04:11:59, longli@...uxonhyperv.com
> > > (longli@...uxonhyperv.com) wrote:
> > > > From: Long Li <longli@...rosoft.com>
> > > >
> > > > When running under Hyper-V, the master device to the RDMA device
> > > > is always bonded to this RDMA device if it's present in the
> > > > kernel. This is not user-configurable.
> > > >
> > > > The master device can be unbind/bind from the kernel. During those
> > > > events, the RDMA device should set to the current netdev to relect
> > > > the change of master device from those events.
> > > >
> > > > Signed-off-by: Long Li <longli@...rosoft.com>
> > > > ---
> > > >  drivers/infiniband/hw/mana/device.c  | 35
> > > > ++++++++++++++++++++++++++++  drivers/infiniband/hw/mana/mana_ib.h
> > > > ++++++++++++++++++++++++++++ |
> > > > 1 +
> > > >  2 files changed, 36 insertions(+)
> > > >
> > > > diff --git a/drivers/infiniband/hw/mana/device.c
> > > > b/drivers/infiniband/hw/mana/device.c
> > > > index 3416a85f8738..3e4f069c2258 100644
> > > > --- a/drivers/infiniband/hw/mana/device.c
> > > > +++ b/drivers/infiniband/hw/mana/device.c
> > > > @@ -51,6 +51,37 @@ static const struct ib_device_ops mana_ib_dev_ops =
> {
> > > >                          ib_ind_table),  };
> > > >
> > > > +static int mana_ib_netdev_event(struct notifier_block *this,
> > > > +                             unsigned long event, void *ptr) {
> > > > +     struct mana_ib_dev *dev = container_of(this, struct mana_ib_dev, nb);
> > > > +     struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
> > > > +     struct gdma_context *gc = dev->gdma_dev->gdma_context;
> > > > +     struct mana_context *mc = gc->mana.driver_data;
> > > > +     struct net_device *ndev;
> > > > +
> > > > +     if (event_dev != mc->ports[0])
> > > > +             return NOTIFY_DONE;
> > > > +
> > > > +     switch (event) {
> > > > +     case NETDEV_CHANGEUPPER:
> > > > +             rcu_read_lock();
> > > > +             ndev = mana_get_primary_netdev_rcu(mc, 0);
> > > > +             rcu_read_unlock();
> > > ...
> > > > +
> > > > +             /*
> > > > +              * RDMA core will setup GID based on updated netdev.
> > > > +              * It's not possible to race with the core as rtnl lock is being
> > > > +              * held.
> > > > +              */
> > > > +             ib_device_set_netdev(&dev->ib_dev, ndev, 1);
> > > rcu_read_unlock() should be here, right ?
> >
> > It can't.  ib_device_set_netdev() is calling alloc_port_data() and may sleep.
> >
> > I think this locking is okay. This event only comes in when:
> > 1. the master device has changed to netvsc. In this case ndev is guaranteed to
> be valid as this notification is triggered by netvsc.
> > 2. the master device has changed to itself (the ethernet device parent for the IB
> device).  In this case, ndev is valid because mana_ib is an auxiliary device to ndev
> and it can't unload itself at this time.
> 
> 
> Why not return with the netdev refcount held so you don't need this weirdo rcu
> thing?
> 
> Jason

I sent v3 with netdev refcount held. Thank you.

Long