Subject: Re: [PATCH net 1/3] net/mlx5e: SD, Fix race condition in secondary device probe/remove

From: Jakub Kicinski <[email-masked]>
Date: Wed, 1 Apr 2026 20:08:42 -0700

On Mon, 30 Mar 2026 22:34:10 +0300 Tariq Toukan wrote:
> From: Shay Drory <[email-masked]>
> 
> When utilizing Socket-Direct single netdev functionality the driver
> resolves the actual auxiliary device using mlx5_sd_get_adev(). However,
> the current implementation returns the primary ETH auxiliary device
> without holding the device lock, leading to a potential race condition
> where the ETH device could be unbound or removed concurrently during
> probe, suspend, resume, or remove operations.[1]
> 
> Fix this by introducing mlx5_sd_put_adev() and updating
> mlx5_sd_get_adev() so that secondaries devices would acquire the device
> lock of the returned auxiliary device. After the lock is acquired, a
> second devcom check is needed[2].
> In addition, update The callers to pair the get operation with the new
> put operation, ensuring the lock is held while the auxiliary device is
> being operated on and released afterwards.

Please explain why the "primary" designation is reliable, and therefore
we can be sure there will be no ABBA deadlock here

> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index b6c12460b54a..5761f655f488 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -6657,8 +6657,11 @@ static int mlx5e_resume(struct auxiliary_device *adev)
>  		return err;
>  
>  	actual_adev = mlx5_sd_get_adev(mdev, adev, edev->idx);
> -	if (actual_adev)
> -		return _mlx5e_resume(actual_adev);
> +	if (actual_adev) {
> +		err = _mlx5e_resume(actual_adev);
> +		mlx5_sd_put_adev(actual_adev, adev);
> +		return err;
> +	}
>  	return 0;

Feels like I recently complained about similar code y'all were trying
to add. Magically and conditionally locking something in a get helper
makes for extremely confusing code.
-- 
pw-bot: cr