Re: [PATCH net 1/2] net/mlx5: HWS, fix reformat pool creation race

[Moshe Shemesh <moshe@nvidia.com>]

On 10/8/2026 11:42 PM, Alexandre Cassen wrote:
> 
> mlx5_fs_get_pr_encap_pool() inserts a new pool when the lookup misses.
> Two callers allocating the first reformat of a size at once both
> create one and the second fails with -EBUSY. TC serializes these
> allocations under encap_tbl_lock while RDMA flow actions on the FDB
> don't.
> 
> Sashiko AI review of an earlier series spotted this issue.
> 
> Tested for regressions on ConnectX-7 with firmware 28.48.1000.
> 
> Fixes: aecd9d1020e3 ("net/mlx5: fs, add HWS packet reformat API function")
> Signed-off-by: Alexandre Cassen <acassen@corp.free.fr>

Reviewed-by: Moshe Shemesh <moshe@nvidia.com>

Thanks.
> ---
>   .../mellanox/mlx5/core/steering/hws/fs_hws.c        | 13 +++++++------
>   1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/steering/hws/fs_hws.c b/drivers/net/ethernet/mellanox/mlx5/core/steering/hws/fs_hws.c
> index 5a172c572a68..66edb42268cb 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/steering/hws/fs_hws.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/steering/hws/fs_hws.c
> @@ -1228,7 +1228,7 @@ static struct mlx5_fs_pool *
>   mlx5_fs_get_pr_encap_pool(struct mlx5_core_dev *dev, struct xarray *pr_pools,
>                            enum mlx5hws_action_type reformat_type, size_t size)
>   {
> -       struct mlx5_fs_pool *pr_pool;
> +       struct mlx5_fs_pool *pr_pool, *old;
>          unsigned long index = size;
>          int err;
> 
> @@ -1242,13 +1242,14 @@ mlx5_fs_get_pr_encap_pool(struct mlx5_core_dev *dev, struct xarray *pr_pools,
>          err = mlx5_fs_hws_pr_pool_init(pr_pool, dev, size, reformat_type);
>          if (err)
>                  goto free_pr_pool;
> -       err = xa_insert(pr_pools, index, pr_pool, GFP_KERNEL);
> -       if (err)
> -               goto cleanup_pr_pool;
> -       return pr_pool;
> +       old = xa_cmpxchg(pr_pools, index, NULL, pr_pool, GFP_KERNEL);
> +       if (!old)
> +               return pr_pool;
> 
> -cleanup_pr_pool:
>          mlx5_fs_hws_pr_pool_cleanup(pr_pool);
> +       kfree(pr_pool);
> +       return xa_is_err(old) ? ERR_PTR(xa_err(old)) : old;
> +
>   free_pr_pool:
>          kfree(pr_pool);
>          return ERR_PTR(err);
> --
> 2.43.0
>