RDMA/mlx5: Fix a race for DMABUF MR which can lead to CQE with error

This patch addresses a potential race condition for a DMABUF MR that can
result in a CQE with an error on the UMR QP.

During the __mlx5_ib_dereg_mr() flow, the following sequence of calls
occurs:
mlx5_revoke_mr()
mlx5r_umr_revoke_mr()
mlx5r_umr_post_send_wait()
At this point, the lkey is freed from the hardware's perspective.

However, concurrently, mlx5_ib_dmabuf_invalidate_cb() might be triggered
by another task attempting to invalidate the MR having that freed lkey.

Since the lkey has already been freed, this can lead to a CQE error,
causing the UMR QP to enter an error state.

To resolve this race condition, the dma_resv_lock() which was hold as
part of the mlx5_ib_dmabuf_invalidate_cb() is now also acquired as part
of the mlx5_revoke_mr() scope.

Upon a successful revoke, we set umem_dmabuf->private which points to
that MR to NULL, preventing any further invalidation attempts on its
lkey.

Fixes: e6fb246 ("RDMA/mlx5: Consolidate MR destruction to mlx5_ib_dereg_mr()")
Signed-off-by: Yishai Hadas <[email protected]>
Reviewed-by: Artemy Kovalyov <[email protected]>
Link: https://patch.msgid.link/70617067abbfaa0c816a2544c922e7f4346def58.1738587016.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <[email protected]>

Author: yishaih

drivers/infiniband/hw/mlx5/mr.c

@@ -1550,7 +1550,7 @@ static void mlx5_ib_dmabuf_invalidate_cb(struct dma_buf_attachment *attach)
 
 	dma_resv_assert_held(umem_dmabuf->attach->dmabuf->resv);
 
-	if (!umem_dmabuf->sgt)
+	if (!umem_dmabuf->sgt || !mr)
 		return;
 
 	mlx5r_umr_update_mr_pas(mr, MLX5_IB_UPD_XLT_ZAP);
@@ -2022,11 +2022,16 @@ static int mlx5_revoke_mr(struct mlx5_ib_mr *mr)
 	struct mlx5_ib_dev *dev = to_mdev(mr->ibmr.device);
 	struct mlx5_cache_ent *ent = mr->mmkey.cache_ent;
 	bool is_odp = is_odp_mr(mr);
+	bool is_odp_dma_buf = is_dmabuf_mr(mr) &&
+			!to_ib_umem_dmabuf(mr->umem)->pinned;
 	int ret = 0;
 
 	if (is_odp)
 		mutex_lock(&to_ib_umem_odp(mr->umem)->umem_mutex);
 
+	if (is_odp_dma_buf)
+		dma_resv_lock(to_ib_umem_dmabuf(mr->umem)->attach->dmabuf->resv, NULL);
+
 	if (mr->mmkey.cacheable && !mlx5r_umr_revoke_mr(mr) && !cache_ent_find_and_store(dev, mr)) {
 		ent = mr->mmkey.cache_ent;
 		/* upon storing to a clean temp entry - schedule its cleanup */
@@ -2054,6 +2059,12 @@ static int mlx5_revoke_mr(struct mlx5_ib_mr *mr)
 		mutex_unlock(&to_ib_umem_odp(mr->umem)->umem_mutex);
 	}
 
+	if (is_odp_dma_buf) {
+		if (!ret)
+			to_ib_umem_dmabuf(mr->umem)->private = NULL;
+		dma_resv_unlock(to_ib_umem_dmabuf(mr->umem)->attach->dmabuf->resv);
+	}
+
 	return ret;
 }