Re: [PATCH net-next v3 15/16] net/mlx5e: take the rtnl lock when calling netif_set_xps_queue
From: Saeed Mahameed <saeed@kernel.org>
Date: 2021-03-12 20:54:53
On Fri, 2021-03-12 at 16:04 +0100, Antoine Tenart wrote:
quoted hunk ↗ jump to hunk
netif_set_xps_queue must be called with the rtnl lock taken, and this is now enforced using ASSERT_RTNL(). mlx5e_attach_netdev was taking the lock conditionally, fix this by taking the rtnl lock all the time. Signed-off-by: Antoine Tenart <atenart@kernel.org> --- drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-)diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.cb/drivers/net/ethernet/mellanox/mlx5/core/en_main.c index ec2fcb2a2977..96cba86b9f0d 100644--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c@@ -5557,7 +5557,6 @@ static void mlx5e_update_features(structnet_device *netdev) int mlx5e_attach_netdev(struct mlx5e_priv *priv) { - const bool take_rtnl = priv->netdev->reg_state == NETREG_REGISTERED; const struct mlx5e_profile *profile = priv->profile; int max_nch; int err;@@ -5578,15 +5577,11 @@ int mlx5e_attach_netdev(struct mlx5e_priv*priv) * 2. Set our default XPS cpumask. * 3. Build the RQT. * - * rtnl_lock is required by netif_set_real_num_*_queues in case the - * netdev has been registered by this point (if this function was called - * in the reload or resume flow). + * rtnl_lock is required by netif_set_xps_queue. */
There is a reason why it is conditional:
we had a bug in the past of double locking here:
[ 4255.283960] echo/644 is trying to acquire lock:
[ 4255.285092] ffffffff85101f90 (rtnl_mutex){+..}, at:
mlx5e_attach_netdev0xd4/0×3d0 [mlx5_core]
[ 4255.287264]
[ 4255.287264] but task is already holding lock:
[ 4255.288971] ffffffff85101f90 (rtnl_mutex){+..}, at:
ipoib_vlan_add0×7c/0×2d0 [ib_ipoib]
ipoib_vlan_add is called under rtnl and will eventually call
mlx5e_attach_netdev, we don't have much control over this in mlx5
driver since the rdma stack provides a per-prepared netdev to attach to
our hw. maybe it is time we had a nested rtnl lock ..
- if (take_rtnl) - rtnl_lock(); + rtnl_lock(); err = mlx5e_num_channels_changed(priv); - if (take_rtnl) - rtnl_unlock(); + rtnl_unlock(); if (err) goto out;