netdev - Re: [PATCH net 2/8] net/mlx5: Fix a lockdep warning as part of the write combining test

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Z4aRvfqeIGAIerDX@lzaremba-mobl.ger.corp.intel.com>
Date: Tue, 14 Jan 2025 17:33:01 +0100
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: Tariq Toukan <tariqt@...dia.com>
CC: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>, "Andrew
 Lunn" <andrew+netdev@...n.ch>, <netdev@...r.kernel.org>, Saeed Mahameed
	<saeedm@...dia.com>, Gal Pressman <gal@...dia.com>, Leon Romanovsky
	<leonro@...dia.com>, Mark Bloch <mbloch@...dia.com>, Moshe Shemesh
	<moshe@...dia.com>, Yishai Hadas <yishaih@...dia.com>, Michael Guralnik
	<michaelgur@...dia.com>
Subject: Re: [PATCH net 2/8] net/mlx5: Fix a lockdep warning as part of the
 write combining test

On Mon, Jan 13, 2025 at 05:40:48PM +0200, Tariq Toukan wrote:
> From: Yishai Hadas <yishaih@...dia.com>
> 
> Fix a lockdep warning [1] observed during the write combining test.
> 
> The warning indicates a potential nested lock scenario that could lead
> to a deadlock.
> 
> However, this is a false positive alarm because the SF lock and its
> parent lock are distinct ones.
> 
> The lockdep confusion arises because the locks belong to the same object
> class (i.e., struct mlx5_core_dev).
> 
> To resolve this, the code has been refactored to avoid taking both
> locks. Instead, only the parent lock is acquired.
> 

[...]

> 
> Fixes: d98995b4bf98 ("net/mlx5: Reimplement write combining test")
> Signed-off-by: Yishai Hadas <yishaih@...dia.com>
> Reviewed-by: Michael Guralnik <michaelgur@...dia.com>
> Signed-off-by: Tariq Toukan <tariqt@...dia.com>

Reviewed-by: Larysa Zaremba <larysa.zaremba@...el.com>

> ---
>  drivers/net/ethernet/mellanox/mlx5/core/wc.c | 24 ++++++++++----------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/wc.c b/drivers/net/ethernet/mellanox/mlx5/core/wc.c
> index 1bed75eca97d..740b719e7072 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/wc.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/wc.c
> @@ -382,6 +382,7 @@ static void mlx5_core_test_wc(struct mlx5_core_dev *mdev)
>  
>  bool mlx5_wc_support_get(struct mlx5_core_dev *mdev)
>  {
> +	struct mutex *wc_state_lock = &mdev->wc_state_lock;
>  	struct mlx5_core_dev *parent = NULL;
>  
>  	if (!MLX5_CAP_GEN(mdev, bf)) {
> @@ -400,32 +401,31 @@ bool mlx5_wc_support_get(struct mlx5_core_dev *mdev)
>  		 */
>  		goto out;
>  
> -	mutex_lock(&mdev->wc_state_lock);
> -
> -	if (mdev->wc_state != MLX5_WC_STATE_UNINITIALIZED)
> -		goto unlock;
> -
>  #ifdef CONFIG_MLX5_SF
> -	if (mlx5_core_is_sf(mdev))
> +	if (mlx5_core_is_sf(mdev)) {
>  		parent = mdev->priv.parent_mdev;
> +		wc_state_lock = &parent->wc_state_lock;
> +	}
>  #endif
>  
> -	if (parent) {
> -		mutex_lock(&parent->wc_state_lock);
> +	mutex_lock(wc_state_lock);
>  
> +	if (mdev->wc_state != MLX5_WC_STATE_UNINITIALIZED)
> +		goto unlock;
> +
> +	if (parent) {
>  		mlx5_core_test_wc(parent);
>  
>  		mlx5_core_dbg(mdev, "parent set wc_state=%d\n",
>  			      parent->wc_state);
>  		mdev->wc_state = parent->wc_state;
>  
> -		mutex_unlock(&parent->wc_state_lock);
> +	} else {
> +		mlx5_core_test_wc(mdev);
>  	}
>  
> -	mlx5_core_test_wc(mdev);
> -
>  unlock:
> -	mutex_unlock(&mdev->wc_state_lock);
> +	mutex_unlock(wc_state_lock);
>  out:
>  	mlx5_core_dbg(mdev, "wc_state=%d\n", mdev->wc_state);
>  
> -- 
> 2.45.0
> 
>