Re: [PATCH 14/15] RDMA/mlx5: Do not race with mlx5_ib_invalidate_range during create and destroy

Jason Gunthorpe
2019-10-28T14:18:47Z

On Wed, Oct 09, 2019 at 01:09:34PM -0300, Jason Gunthorpe wrote:
> diff --git a/drivers/infiniband/hw/mlx5/odp.c b/drivers/infiniband/hw/mlx5/odp.c
> index 66523313c3e46c..fd2306aff78ad7 100644
> +++ b/drivers/infiniband/hw/mlx5/odp.c
> @@ -144,6 +144,32 @@ void mlx5_odp_populate_klm(struct mlx5_klm *pklm, size_t idx, size_t nentries,
> }
> }
>
> +static void dma_fence_odp_mr(struct mlx5_ib_mr *mr)
> +{
> + struct ib_umem_odp *odp = to_ib_umem_odp(mr->umem);
> +
> + /* Ensure mlx5_ib_invalidate_range() will not touch the MR any more */
> + mutex_lock(&odp->umem_mutex);
> + if (odp->npages) {
> + /*
> + * If not cached then the caller had to do clean_mrs first to
> + * fence the mkey.
> + */
> + if (mr->allocated_from_cache) {
> + mlx5_mr_cache_invalidate(mr);
> + } else {
> + /* clean_mr() */
> + mlx5_core_destroy_mkey(mr->dev->mdev, &mr->mmkey);
> + WARN_ON(mr->descs);
> + }
> + ib_umem_odp_unmap_dma_pages(odp, ib_umem_start(odp),
> + ib_umem_end(odp));
> + WARN_ON(odp->npages);
> + }
> + odp->private = NULL;
> + mutex_unlock(&odp->umem_mutex);

The new mmu notifier debugging catches that mlx5_core_destroy_mkey()
allocates as GFP_KERNEL and cannot be called under umem_mutex, so this
needs to be reworked.

I think to rely on mlx5_mr_cache_invalidate() to fence the DMA, then
destroy out of the lock:

diff --git a/drivers/infiniband/hw/mlx5/odp.c b/drivers/infiniband/hw/mlx5/odp.c
index 74c45356d54007..f713eb82eeead4 100644
--- a/drivers/infiniband/hw/mlx5/odp.c
+++ b/drivers/infiniband/hw/mlx5/odp.c
@@ -151,23 +151,18 @@ static void dma_fence_odp_mr(struct mlx5_ib_mr *mr)
/* Ensure mlx5_ib_invalidate_range() will not touch the MR any more */
mutex_lock(&odp->umem_mutex);
if (odp->npages) {
- /*
- * If not cached then the caller had to do clean_mrs first to
- * fence the mkey.
- */
- if (mr->allocated_from_cache) {
- mlx5_mr_cache_invalidate(mr);
- } else {
- /* clean_mr() */
- mlx5_core_destroy_mkey(mr->dev->mdev, &mr->mmkey);
- WARN_ON(mr->descs);
- }
+ mlx5_mr_cache_invalidate(mr);
ib_umem_odp_unmap_dma_pages(odp, ib_umem_start(odp),
ib_umem_end(odp));
WARN_ON(odp->npages);
}
odp->private = NULL;
mutex_unlock(&odp->umem_mutex);
+
+ if (!mr->allocated_from_cache) {
+ mlx5_core_destroy_mkey(mr->dev->mdev, &mr->mmkey);
+ WARN_ON(mr->descs);
+ }
}

/*