Workloads that repeatedly allocate and release mkeys carrying TPH
steering-tag hints (e.g. churning RDMA MRs) leak one
struct mlx5_st_idx_data per cycle; kmemleak flags it as unreferenced
and the kmalloc slab grows over time.

When the last reference to an ST table entry is dropped,
mlx5_st_dealloc_index() removed the entry from idx_xa but the backing
mlx5_st_idx_data allocation was never freed.

Free idx_data after the xa_erase() so the lifetime of the bookkeeping
struct matches the lifetime of the ST entry it tracks.

Cc: stable@vger.kernel.org
Fixes: 888a7776f4fb ("net/mlx5: Add support for device steering tag")
Reviewed-by: Michael Gur <redacted>
Signed-off-by: Zhiping Zhang <redacted>
---
v2: respin per maintainer-netdev.rst; no code change.
v1: https://lore.kernel.org/linux-rdma/20260612170406.3339093-1-zhipingz@meta.com/ (local)

  drivers/net/ethernet/mellanox/mlx5/core/lib/st.c | 1 +
  1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/st.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/st.c
index 997be91f0a13..7cedc348790d 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/st.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/st.c

@@ -175,6 +175,7 @@ int mlx5_st_dealloc_index(struct mlx5_core_dev *dev, u16 st_index)
  
  	if (refcount_dec_and_test(&idx_data->usecount)) {
  		xa_erase(&st->idx_xa, st_index);
+		kfree(idx_data);
  		/* We leave PCI config space as was before, no mkey will refer to it */
  	}