devlink: change per-devlink netdev notifier to static one

The commit 565b4824c3 ("devlink: change port event netdev notifier
from per-net to global") changed original per-net notifier to be
per-devlink instance. That fixed the issue of non-receiving events
of netdev uninit if that moved to a different namespace.
That worked fine in -net tree.

However, later on when commit ee75f1fc44 ("net/mlx5e: Create
separate devlink instance for ethernet auxiliary device") and
commit 72ed5d5624 ("net/mlx5: Suspend auxiliary devices only in
case of PCI device suspend") were merged, a deadlock was introduced
when removing a namespace with devlink instance with another nested
instance.

Here there is the bad flow example resulting in deadlock with mlx5:
net_cleanup_work -> cleanup_net (takes down_read(&pernet_ops_rwsem) ->
devlink_pernet_pre_exit() -> devlink_reload() ->
mlx5_devlink_reload_down() -> mlx5_unload_one_devl_locked() ->
mlx5_detach_device() -> del_adev() -> mlx5e_remove() ->
mlx5e_destroy_devlink() -> devlink_free() ->
unregister_netdevice_notifier() (takes down_write(&pernet_ops_rwsem)

Steps to reproduce:
$ modprobe mlx5_core
$ ip netns add ns1
$ devlink dev reload pci/0000:08:00.0 netns ns1
$ ip netns del ns1

Resolve this by converting the notifier from per-devlink instance to
a static one registered during init phase and leaving it registered
forever. Use this notifier for all devlink port instances created
later on.

Note what a tree needs this fix only in case all of the cited fixes
commits are present.

Reported-by: Moshe Shemesh <moshe@nvidia.com>
Fixes: 565b4824c3 ("devlink: change port event netdev notifier from per-net to global")
Fixes: ee75f1fc44 ("net/mlx5e: Create separate devlink instance for ethernet auxiliary device")
Fixes: 72ed5d5624 ("net/mlx5: Suspend auxiliary devices only in case of PCI device suspend")
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230510144621.932017-1-jiri@resnulli.us
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/devlink/core.c

@@ -204,11 +204,6 @@ struct devlink *devlink_alloc_ns(const struct devlink_ops *ops,
 	if (ret < 0)
 		goto err_xa_alloc;
 
-	devlink->netdevice_nb.notifier_call = devlink_port_netdevice_event;
-	ret = register_netdevice_notifier(&devlink->netdevice_nb);
-	if (ret)
-		goto err_register_netdevice_notifier;
-
 	devlink->dev = dev;
 	devlink->ops = ops;
 	xa_init_flags(&devlink->ports, XA_FLAGS_ALLOC);
@@ -233,8 +228,6 @@ struct devlink *devlink_alloc_ns(const struct devlink_ops *ops,
 
 	return devlink;
 
-err_register_netdevice_notifier:
-	xa_erase(&devlinks, devlink->index);
 err_xa_alloc:
 	kfree(devlink);
 	return NULL;
@@ -266,8 +259,6 @@ void devlink_free(struct devlink *devlink)
 	xa_destroy(&devlink->params);
 	xa_destroy(&devlink->ports);
 
-	WARN_ON_ONCE(unregister_netdevice_notifier(&devlink->netdevice_nb));
-
 	xa_erase(&devlinks, devlink->index);
 
 	devlink_put(devlink);
@@ -303,6 +294,10 @@ static struct pernet_operations devlink_pernet_ops __net_initdata = {
 	.pre_exit = devlink_pernet_pre_exit,
 };
 
+static struct notifier_block devlink_port_netdevice_nb __net_initdata = {
+	.notifier_call = devlink_port_netdevice_event,
+};
+
 static int __init devlink_init(void)
 {
 	int err;
@@ -311,6 +306,9 @@ static int __init devlink_init(void)
 	if (err)
 		goto out;
 	err = register_pernet_subsys(&devlink_pernet_ops);
+	if (err)
+		goto out;
+	err = register_netdevice_notifier(&devlink_port_netdevice_nb);
 
 out:
 	WARN_ON(err);

net/devlink/devl_internal.h

@@ -50,7 +50,6 @@ struct devlink {
 	u8 reload_failed:1;
 	refcount_t refcount;
 	struct rcu_work rwork;
-	struct notifier_block netdevice_nb;
 	char priv[] __aligned(NETDEV_ALIGN);
 };
 

net/devlink/leftover.c

@@ -7073,10 +7073,9 @@ int devlink_port_netdevice_event(struct notifier_block *nb,
 	struct devlink_port *devlink_port = netdev->devlink_port;
 	struct devlink *devlink;
 
-	devlink = container_of(nb, struct devlink, netdevice_nb);
-
-	if (!devlink_port || devlink_port->devlink != devlink)
+	if (!devlink_port)
 		return NOTIFY_OK;
+	devlink = devlink_port->devlink;
 
 	switch (event) {
 	case NETDEV_POST_INIT: