[PATCH 12/15] RDMA/mlx5: Rework implicit ODP destroy

Jason Gunthorpe
2019-10-09T16:36:17Z

Use SRCU in a sensible way by removing all MRs in the implicit tree from
the two xarrays (the update operation), then a synchronize, followed by a
normal single threaded teardown.

This is only a little unusual from the normal pattern as there can still
be some work pending in the unbound wq that may also require a workqueue
flush. This is tracked with a single atomic, consolidating the redundant
existing atomics and wait queue.

For understand-ability the entire ODP implicit create/destroy flow now
largely exists in a single pair of functions within odp.c, with a few
support functions for tearing down an unused child.

Reviewed-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
drivers/infiniband/hw/mlx5/main.c | 2 -
drivers/infiniband/hw/mlx5/mlx5_ib.h | 9 +-
drivers/infiniband/hw/mlx5/mr.c | 21 ++--
drivers/infiniband/hw/mlx5/odp.c | 152 ++++++++++++++++++---------
include/rdma/ib_umem_odp.h | 2 -
5 files changed, 120 insertions(+), 66 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index 4692c37b057cee..add24b6289004a 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -6146,8 +6146,6 @@ static void mlx5_ib_stage_init_cleanup(struct mlx5_ib_dev *dev)
{
mlx5_ib_cleanup_multiport_master(dev);
WARN_ON(!xa_empty(&dev->odp_mkeys));
- if (IS_ENABLED(CONFIG_INFINIBAND_ON_DEMAND_PAGING))
- srcu_barrier(&dev->odp_srcu);
cleanup_srcu_struct(&dev->odp_srcu);

WARN_ON(!xa_empty(&dev->sig_mrs));
diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
index 88769fcffb5a10..b8c958f6262848 100644
--- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
@@ -618,10 +618,13 @@ struct mlx5_ib_mr {
u64 pi_iova;

/* For ODP and implicit */
- atomic_t num_leaf_free;
- wait_queue_head_t q_leaf_free;
- atomic_t num_pending_prefetch;
+ atomic_t num_deferred_work;
struct xarray implicit_children;
+ union {
+ struct rcu_head rcu;
+ struct list_head elm;
+ struct work_struct work;
+ } odp_destroy;

struct mlx5_async_work cb_work;
};
diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
index fd94838a8845d5..1e91f61efa8a3e 100644
--- a/drivers/infiniband/hw/mlx5/mr.c
+++ b/drivers/infiniband/hw/mlx5/mr.c
@@ -1317,7 +1317,7 @@ struct ib_mr *mlx5_ib_reg_user_mr(struct ib_pd *pd, u64 start, u64 length,

if (is_odp_mr(mr)) {
to_ib_umem_odp(mr->umem)->private = mr;
- atomic_set(&mr->num_pending_prefetch, 0);
+ atomic_set(&mr->num_deferred_work, 0);
err = xa_err(xa_store(&dev->odp_mkeys,
mlx5_base_mkey(mr->mmkey.key), &mr->mmkey,
GFP_KERNEL));
@@ -1573,17 +1573,15 @@ static void dereg_mr(struct mlx5_ib_dev *dev, struct mlx5_ib_mr *mr)
synchronize_srcu(&dev->odp_srcu);

/* dequeue pending prefetch requests for the mr */
- if (atomic_read(&mr->num_pending_prefetch))
+ if (atomic_read(&mr->num_deferred_work)) {
flush_workqueue(system_unbound_wq);
- WARN_ON(atomic_read(&mr->num_pending_prefetch));
+ WARN_ON(atomic_read(&mr->num_deferred_work));
+ }

/* Destroy all page mappings */
- if (!umem_odp->is_implicit_odp)
- mlx5_ib_invalidate_range(umem_odp,
- ib_umem_start(umem_odp),
- ib_umem_end(umem_odp));
- else
- mlx5_ib_free_implicit_mr(mr);
+ mlx5_ib_invalidate_range(umem_odp, ib_umem_start(umem_odp),
+ ib_umem_end(umem_odp));
+
/*
* We kill the umem before the MR for ODP,
* so that there will not be any invalidations in
@@ -1620,6 +1618,11 @@ int mlx5_ib_dereg_mr(struct ib_mr *ibmr, struct ib_udata *udata)
dereg_mr(to_mdev(mmr->klm_mr->ibmr.device), mmr->klm_mr);
}

+ if (is_odp_mr(mmr) && to_ib_umem_odp(mmr->umem)->is_implicit_odp) {
+ mlx5_ib_free_implicit_mr(mmr);
+ return 0;
+ }
+
dereg_mr(to_mdev(ibmr->device), mmr);

return 0;
diff --git a/drivers/infiniband/hw/mlx5/odp.c b/drivers/infiniband/hw/mlx5/odp.c
index 1897ce6a25f693..71f8580b25b2ab 100644
--- a/drivers/infiniband/hw/mlx5/odp.c
+++ b/drivers/infiniband/hw/mlx5/odp.c
@@ -144,31 +144,79 @@ void mlx5_odp_populate_klm(struct mlx5_klm *pklm, size_t idx, size_t nentries,
}
}

-static void mr_leaf_free_action(struct work_struct *work)
+/*
+ * This must be called after the mr has been removed from implicit_children
+ * and odp_mkeys and the SRCU synchronized. NOTE: The MR does not necessarily
+ * have to be empty here, parallel page faults could have raced with the free
+ * process and added pages to it.
+ */
+static void free_implicit_child_mr(struct mlx5_ib_mr *mr, bool need_imr_xlt)
{
- struct ib_umem_odp *odp = container_of(work, struct ib_umem_odp, work);
- int idx = ib_umem_start(odp) >> MLX5_IMR_MTT_SHIFT;
- struct mlx5_ib_mr *mr = odp->private, *imr = mr->parent;
+ struct mlx5_ib_mr *imr = mr->parent;
struct ib_umem_odp *odp_imr = to_ib_umem_odp(imr->umem);
+ struct ib_umem_odp *odp = to_ib_umem_odp(mr->umem);
+ unsigned long idx = ib_umem_start(odp) >> MLX5_IMR_MTT_SHIFT;
int srcu_key;

- mr->parent = NULL;
- synchronize_srcu(&mr->dev->odp_srcu);
+ /* implicit_child_mr's are not allowed to have deferred work */
+ WARN_ON(atomic_read(&mr->num_deferred_work));

- if (xa_load(&mr->dev->odp_mkeys, mlx5_base_mkey(imr->mmkey.key))) {
+ if (need_imr_xlt) {
srcu_key = srcu_read_lock(&mr->dev->odp_srcu);
mutex_lock(&odp_imr->umem_mutex);
- mlx5_ib_update_xlt(imr, idx, 1, 0,
+ mlx5_ib_update_xlt(mr->parent, idx, 1, 0,
MLX5_IB_UPD_XLT_INDIRECT |
MLX5_IB_UPD_XLT_ATOMIC);
mutex_unlock(&odp_imr->umem_mutex);
srcu_read_unlock(&mr->dev->odp_srcu, srcu_key);
}
- ib_umem_odp_release(odp);
+
+ mr->parent = NULL;
mlx5_mr_cache_free(mr->dev, mr);
+ ib_umem_odp_release(odp);
+ atomic_dec(&imr->num_deferred_work);
+}
+
+static void free_implicit_child_mr_work(struct work_struct *work)
+{
+ struct mlx5_ib_mr *mr =
+ container_of(work, struct mlx5_ib_mr, odp_destroy.work);
+
+ free_implicit_child_mr(mr, true);
+}
+
+static void free_implicit_child_mr_rcu(struct rcu_head *head)
+{
+ struct mlx5_ib_mr *mr =
+ container_of(head, struct mlx5_ib_mr, odp_destroy.rcu);
+
+ /* Freeing a MR is a sleeping operation, so bounce to a work queue */
+ INIT_WORK(&mr->odp_destroy.work, free_implicit_child_mr_work);
+ queue_work(system_unbound_wq, &mr->odp_destroy.work);
+}
+
+static void destroy_unused_implicit_child_mr(struct mlx5_ib_mr *mr)
+{
+ struct ib_umem_odp *odp = to_ib_umem_odp(mr->umem);
+ unsigned long idx = ib_umem_start(odp) >> MLX5_IMR_MTT_SHIFT;
+ struct mlx5_ib_mr *imr = mr->parent;

- if (atomic_dec_and_test(&imr->num_leaf_free))
- wake_up(&imr->q_leaf_free);
+ xa_lock(&imr->implicit_children);
+ /*
+ * This can race with mlx5_ib_free_implicit_mr(), the first one to
+ * reach the xa lock wins the race and destroys the MR.
+ */
+ if (__xa_cmpxchg(&imr->implicit_children, idx, mr, NULL, GFP_ATOMIC) !=
+ mr)
+ goto out_unlock;
+
+ __xa_erase(&mr->dev->odp_mkeys, mlx5_base_mkey(mr->mmkey.key));
+ atomic_inc(&imr->num_deferred_work);
+ call_srcu(&mr->dev->odp_srcu, &mr->odp_destroy.rcu,
+ free_implicit_child_mr_rcu);
+
+out_unlock:
+ xa_unlock(&imr->implicit_children);
}

void mlx5_ib_invalidate_range(struct ib_umem_odp *umem_odp, unsigned long start,
@@ -240,15 +288,8 @@ void mlx5_ib_invalidate_range(struct ib_umem_odp *umem_odp, unsigned long start,

ib_umem_odp_unmap_dma_pages(umem_odp, start, end);

- if (unlikely(!umem_odp->npages && mr->parent &&
- !umem_odp->dying)) {
- xa_erase(&mr->parent->implicit_children,
- ib_umem_start(umem_odp) >> MLX5_IMR_MTT_SHIFT);
- xa_erase(&mr->dev->odp_mkeys, mlx5_base_mkey(mr->mmkey.key));
- umem_odp->dying = 1;
- atomic_inc(&mr->parent->num_leaf_free);
- schedule_work(&umem_odp->work);
- }
+ if (unlikely(!umem_odp->npages && mr->parent))
+ destroy_unused_implicit_child_mr(mr);
mutex_unlock(&umem_odp->umem_mutex);
}

@@ -375,7 +416,6 @@ static struct mlx5_ib_mr *implicit_get_child_mr(struct mlx5_ib_mr *imr,
mr->mmkey.iova = idx * MLX5_IMR_MTT_SIZE;
mr->parent = imr;
odp->private = mr;
- INIT_WORK(&odp->work, mr_leaf_free_action);

err = mlx5_ib_update_xlt(mr, 0,
MLX5_IMR_MTT_ENTRIES,
@@ -391,7 +431,11 @@ static struct mlx5_ib_mr *implicit_get_child_mr(struct mlx5_ib_mr *imr,
* Once the store to either xarray completes any error unwind has to
* use synchronize_srcu(). Avoid this with xa_reserve()
*/
- ret = xa_cmpxchg(&imr->implicit_children, idx, NULL, mr, GFP_KERNEL);
+ ret = xa_cmpxchg(&imr->implicit_children, idx, NULL, mr,
+ GFP_KERNEL);
+ if (likely(!ret))
+ xa_store(&imr->dev->odp_mkeys, mlx5_base_mkey(mr->mmkey.key),
+ &mr->mmkey, GFP_ATOMIC);
if (unlikely(ret)) {
if (xa_is_err(ret)) {
ret = ERR_PTR(xa_err(ret));
@@ -404,9 +448,6 @@ static struct mlx5_ib_mr *implicit_get_child_mr(struct mlx5_ib_mr *imr,
goto out_release;
}

- xa_store(&imr->dev->odp_mkeys, mlx5_base_mkey(mr->mmkey.key),
- &mr->mmkey, GFP_ATOMIC);
-
mlx5_ib_dbg(imr->dev, "key %x mr %p\n", mr->mmkey.key, mr);
return mr;

@@ -445,9 +486,7 @@ struct mlx5_ib_mr *mlx5_ib_alloc_implicit_mr(struct mlx5_ib_pd *pd,
imr->ibmr.lkey = imr->mmkey.key;
imr->ibmr.rkey = imr->mmkey.key;
imr->umem = &umem_odp->umem;
- init_waitqueue_head(&imr->q_leaf_free);
- atomic_set(&imr->num_leaf_free, 0);
- atomic_set(&imr->num_pending_prefetch, 0);
+ atomic_set(&imr->num_deferred_work, 0);
xa_init(&imr->implicit_children);

err = mlx5_ib_update_xlt(imr, 0,
@@ -477,35 +516,48 @@ struct mlx5_ib_mr *mlx5_ib_alloc_implicit_mr(struct mlx5_ib_pd *pd,
void mlx5_ib_free_implicit_mr(struct mlx5_ib_mr *imr)
{
struct ib_umem_odp *odp_imr = to_ib_umem_odp(imr->umem);
+ struct mlx5_ib_dev *dev = imr->dev;
+ struct list_head destroy_list;
struct mlx5_ib_mr *mtt;
+ struct mlx5_ib_mr *tmp;
unsigned long idx;

- mutex_lock(&odp_imr->umem_mutex);
- xa_for_each (&imr->implicit_children, idx, mtt) {
- struct ib_umem_odp *umem_odp = to_ib_umem_odp(mtt->umem);
+ INIT_LIST_HEAD(&destroy_list);

- xa_erase(&imr->implicit_children, idx);
+ xa_erase(&dev->odp_mkeys, mlx5_base_mkey(imr->mmkey.key));
+ /*
+ * This stops the SRCU protected page fault path from touching either
+ * the imr or any children. The page fault path can only reach the
+ * children xarray via the imr.
+ */
+ synchronize_srcu(&dev->odp_srcu);

- mutex_lock(&umem_odp->umem_mutex);
- ib_umem_odp_unmap_dma_pages(umem_odp, ib_umem_start(umem_odp),
- ib_umem_end(umem_odp));
+ xa_lock(&imr->implicit_children);
+ xa_for_each (&imr->implicit_children, idx, mtt) {
+ __xa_erase(&imr->implicit_children, idx);
+ __xa_erase(&dev->odp_mkeys, mlx5_base_mkey(mtt->mmkey.key));
+ list_add(&mtt->odp_destroy.elm, &destroy_list);
+ }
+ xa_unlock(&imr->implicit_children);

- if (umem_odp->dying) {
- mutex_unlock(&umem_odp->umem_mutex);
- continue;
- }
+ /* Fence access to the child pointers via the pagefault thread */
+ synchronize_srcu(&dev->odp_srcu);

- umem_odp->dying = 1;
- atomic_inc(&imr->num_leaf_free);
- schedule_work(&umem_odp->work);
- mutex_unlock(&umem_odp->umem_mutex);
+ /*
+ * num_deferred_work can only be incremented inside the odp_srcu, or
+ * under xa_lock while the child is in the xarray. Thus at this point
+ * it is only decreasing, and all work holding it is now on the wq.
+ */
+ if (atomic_read(&imr->num_deferred_work)) {
+ flush_workqueue(system_unbound_wq);
+ WARN_ON(atomic_read(&imr->num_deferred_work));
}
- mutex_unlock(&odp_imr->umem_mutex);

- wait_event(imr->q_leaf_free, !atomic_read(&imr->num_leaf_free));
- WARN_ON(!xa_empty(&imr->implicit_children));
- /* Remove any left over reserved elements */
- xa_destroy(&imr->implicit_children);
+ list_for_each_entry_safe (mtt, tmp, &destroy_list, odp_destroy.elm)
+ free_implicit_child_mr(mtt, false);
+
+ mlx5_mr_cache_free(dev, imr);
+ ib_umem_odp_release(odp_imr);
}

#define MLX5_PF_FLAGS_DOWNGRADE BIT(1)
@@ -1579,7 +1631,7 @@ static void destroy_prefetch_work(struct prefetch_mr_work *work)
u32 i;

for (i = 0; i < work->num_sge; ++i)
- atomic_dec(&work->frags[i].mr->num_pending_prefetch);
+ atomic_dec(&work->frags[i].mr->num_deferred_work);
kvfree(work);
}

@@ -1658,7 +1710,7 @@ static bool init_prefetch_work(struct ib_pd *pd,
}

/* Keep the MR pointer will valid outside the SRCU */
- atomic_inc(&work->frags[i].mr->num_pending_prefetch);
+ atomic_inc(&work->frags[i].mr->num_deferred_work);
}
work->num_sge = num_sge;
return true;
diff --git a/include/rdma/ib_umem_odp.h b/include/rdma/ib_umem_odp.h
index 28078efc38339f..09b0e4494986a9 100644
--- a/include/rdma/ib_umem_odp.h
+++ b/include/rdma/ib_umem_odp.h
@@ -78,9 +78,7 @@ struct ib_umem_odp {
bool is_implicit_odp;

struct completion notifier_completion;
- int dying;
unsigned int page_shift;
- struct work_struct work;
};

static inline struct ib_umem_odp *to_ib_umem_odp(struct ib_umem *umem)
--
2.23.0