[PATCH net-next v1 2/4] net/mlx5: Don't free the WC test CQ if destroying it fails

[Yuho Choi <oss.patchbox@gmail.com>]

mlx5_wc_destroy_cq() ignores the result of mlx5_core_destroy_cq() and
frees the CQ buffer and doorbell record anyway, and mlx5_core_test_wc()
then frees the struct mlx5_wc_sq that embeds the CQ. If DESTROY_CQ
fails, the CQ may still exist in firmware and retain access to its
buffer and doorbell record. mlx5_core_destroy_cq() also returns early in
that case, without waiting for EQ handlers that may already hold a
reference to the CQ.

Return the error from mlx5_wc_destroy_cq() and keep both the buffer and
the struct mlx5_wc_sq when it fails, as the regular mlx5_ib CQ destroy
path does. A device in internal error is not affected, since the mlx5
core reports success for DESTROY_CQ in that state.

Fixes: d98995b4bf98 ("net/mlx5: Reimplement write combining test")
Assisted-by: LLM
Signed-off-by: Yuho Choi <oss.patchbox@gmail.com>
---
This was found with a static analysis tool from ongoing, not yet
published research, and confirmed by code inspection. It has not been
reproduced on hardware.

 drivers/net/ethernet/mellanox/mlx5/core/wc.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/wc.c b/drivers/net/ethernet/mellanox/mlx5/core/wc.c
index 7d3d4d739e2cd..df1b1555ed8f4 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/wc.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/wc.c
@@ -148,10 +148,14 @@ static int mlx5_wc_create_cq(struct mlx5_core_dev *mdev, struct mlx5_wc_cq *cq)
 	return err;
 }
 
-static void mlx5_wc_destroy_cq(struct mlx5_wc_cq *cq)
+static int mlx5_wc_destroy_cq(struct mlx5_wc_cq *cq)
 {
-	mlx5_core_destroy_cq(cq->mdev, &cq->mcq);
-	mlx5_wq_destroy(&cq->wq_ctrl);
+	int err = mlx5_core_destroy_cq(cq->mdev, &cq->mcq);
+
+	/* The device may still access an undestroyed CQ's buffer; keep it. */
+	if (!err)
+		mlx5_wq_destroy(&cq->wq_ctrl);
+	return err;
 }
 
 static int create_wc_sq(struct mlx5_core_dev *mdev, void *sqc_data,
@@ -360,6 +364,7 @@ static int mlx5_wc_poll_cq(struct mlx5_wc_sq *sq)
 static void mlx5_core_test_wc(struct mlx5_core_dev *mdev)
 {
 	unsigned int offset = 0;
+	bool keep_sq = false;
 	struct mlx5_wc_sq *sq;
 	int i, err;
 
@@ -396,11 +401,13 @@ static void mlx5_core_test_wc(struct mlx5_core_dev *mdev)
 	mlx5_wc_destroy_sq(sq);
 
 err_create_sq:
-	mlx5_wc_destroy_cq(&sq->cq);
+	/* An undestroyed CQ may still be in use; keep the SQ that holds it. */
+	keep_sq = mlx5_wc_destroy_cq(&sq->cq);
 err_create_cq:
 	mlx5_free_bfreg(mdev, &sq->bfreg);
 err_alloc_bfreg:
-	kfree(sq);
+	if (!keep_sq)
+		kfree(sq);
 
 	if (mdev->wc_state == MLX5_WC_STATE_UNSUPPORTED)
 		mlx5_core_warn(mdev, "Write combining is not supported\n");
-- 
2.43.0