linux-kernel - [PATCH 5.4 131/135] net/mlx5: Fix sleep while atomic in mlx5_eswitch_get

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Date:   Thu, 27 Feb 2020 14:37:51 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Huy Nguyen <huyn@...lanox.com>,
        Mark Bloch <markb@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: [PATCH 5.4 131/135] net/mlx5: Fix sleep while atomic in mlx5_eswitch_get_vepa

From: Huy Nguyen <huyn@...lanox.com>

commit 3d9c5e023a0dbf3e117bb416cfefd9405bf5af0c upstream.

rtnl_bridge_getlink is protected by rcu lock, so mlx5_eswitch_get_vepa
cannot take mutex lock. Two possible issues can happen:
1. User at the same time change vepa mode via RTM_SETLINK command.
2. User at the same time change the switchdev mode via devlink netlink
interface.

Case 1 cannot happen because rtnl executes one message in order.
Case 2 can happen but we do not expect user to change the switchdev mode
when changing vepa. Even if a user does it, so he will read a value
which is no longer valid.

Fixes: 8da202b24913 ("net/mlx5: E-Switch, Add support for VEPA in legacy mode.")
Signed-off-by: Huy Nguyen <huyn@...lanox.com>
Reviewed-by: Mark Bloch <markb@...lanox.com>
Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/ethernet/mellanox/mlx5/core/eswitch.c |   14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

--- a/drivers/net/ethernet/mellanox/mlx5/core/eswitch.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/eswitch.c
@@ -2319,25 +2319,17 @@ out:
 
 int mlx5_eswitch_get_vepa(struct mlx5_eswitch *esw, u8 *setting)
 {
-	int err = 0;
-
 	if (!esw)
 		return -EOPNOTSUPP;
 
 	if (!ESW_ALLOWED(esw))
 		return -EPERM;
 
-	mutex_lock(&esw->state_lock);
-	if (esw->mode != MLX5_ESWITCH_LEGACY) {
-		err = -EOPNOTSUPP;
-		goto out;
-	}
+	if (esw->mode != MLX5_ESWITCH_LEGACY)
+		return -EOPNOTSUPP;
 
 	*setting = esw->fdb_table.legacy.vepa_uplink_rule ? 1 : 0;
-
-out:
-	mutex_unlock(&esw->state_lock);
-	return err;
+	return 0;
 }
 
 int mlx5_eswitch_set_vport_trust(struct mlx5_eswitch *esw,