netdev - [net-next 1/4] net/mlx5: Use a separate work queue for fib event handling

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Message-Id: <20200330071655.169823-2-saeedm@mellanox.com>
Date:   Mon, 30 Mar 2020 00:16:52 -0700
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "David S. Miller" <davem@...emloft.net>, kuba@...nel.org
Cc:     netdev@...r.kernel.org, Mark Zhang <markz@...lanox.com>,
        Roi Dayan <roid@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: [net-next 1/4] net/mlx5: Use a separate work queue for fib event handling

From: Mark Zhang <markz@...lanox.com>

In VF lag mode when remove the bonding module without bring down the
bond device first, we could potentially have circular dependency when we
unload IB devices and also handle fib events:
1. The bond work starts first;
2. The "modprobe -rv bonding" process tries to release the bond device,
   with the "pernet_ops_rwsem" lock hold;
3. The bond work blocks in unregister_netdevice_notifier() and waits for
the lock because fib event came right before;
4. The kernel fib module tries to free all the fib entries by broadcasting
   the "FIB_EVENT_NH_DEL" event;
5. Upon the fib event this lag_mp module holds the fib lock and queue a
   fib work.
So:
   bond work -> modprobe task -> kernel fib module -> lag_mp -> bond work

Today we either reload IB devices in roce lag in nic mode or either handle
fib events in switchdev mode, but a new feature could change that we'll
need to reload IB devices also in switchdev mode so this is a future proof
fix as one may not notice this later.

Signed-off-by: Mark Zhang <markz@...lanox.com>
Reviewed-by: Roi Dayan <roid@...lanox.com>
Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/lag_mp.c | 14 ++++++++++----
 drivers/net/ethernet/mellanox/mlx5/core/lag_mp.h |  1 +
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lag_mp.c b/drivers/net/ethernet/mellanox/mlx5/core/lag_mp.c
index 416676c35b1f..e9089a793632 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lag_mp.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lag_mp.c
@@ -93,9 +93,8 @@ static void mlx5_lag_set_port_affinity(struct mlx5_lag *ldev,
 static void mlx5_lag_fib_event_flush(struct notifier_block *nb)
 {
 	struct lag_mp *mp = container_of(nb, struct lag_mp, fib_nb);
-	struct mlx5_lag *ldev = container_of(mp, struct mlx5_lag, lag_mp);
 
-	flush_workqueue(ldev->wq);
+	flush_workqueue(mp->wq);
 }
 
 struct mlx5_fib_event_work {
@@ -293,7 +292,7 @@ static int mlx5_lag_fib_event(struct notifier_block *nb,
 		return NOTIFY_DONE;
 	}
 
-	queue_work(ldev->wq, &fib_work->work);
+	queue_work(mp->wq, &fib_work->work);
 
 	return NOTIFY_DONE;
 }
@@ -306,11 +305,17 @@ int mlx5_lag_mp_init(struct mlx5_lag *ldev)
 	if (mp->fib_nb.notifier_call)
 		return 0;
 
+	mp->wq = create_singlethread_workqueue("mlx5_lag_mp");
+	if (!mp->wq)
+		return -ENOMEM;
+
 	mp->fib_nb.notifier_call = mlx5_lag_fib_event;
 	err = register_fib_notifier(&init_net, &mp->fib_nb,
 				    mlx5_lag_fib_event_flush, NULL);
-	if (err)
+	if (err) {
+		destroy_workqueue(mp->wq);
 		mp->fib_nb.notifier_call = NULL;
+	}
 
 	return err;
 }
@@ -323,5 +328,6 @@ void mlx5_lag_mp_cleanup(struct mlx5_lag *ldev)
 		return;
 
 	unregister_fib_notifier(&init_net, &mp->fib_nb);
+	destroy_workqueue(mp->wq);
 	mp->fib_nb.notifier_call = NULL;
 }
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lag_mp.h b/drivers/net/ethernet/mellanox/mlx5/core/lag_mp.h
index 79be89e9c7a4..258ac7b2964e 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lag_mp.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lag_mp.h
@@ -16,6 +16,7 @@ enum mlx5_lag_port_affinity {
 struct lag_mp {
 	struct notifier_block     fib_nb;
 	struct fib_info           *mfi; /* used in tracking fib events */
+	struct workqueue_struct   *wq;
 };
 
 #ifdef CONFIG_MLX5_ESWITCH
-- 
2.25.1