From: Jason Gunthorpe <jgg@xxxxxxxxxx>
[ Upstream commit a862192e9227ad46e0447fd0a03869ba1b30d16f ]
Prefetch work in mlx5_ib_prefetch_mr_work can be queued and able to run
concurrently with destruction of the implicit MR. The num_deferred_work
was intended to serialize this, but there is a race:
CPU0 CPU1
mlx5_ib_free_implicit_mr()
xa_erase(odp_mkeys)
synchronize_srcu()
__xa_erase(implicit_children)
mlx5_ib_prefetch_mr_work()
pagefault_mr()
pagefault_implicit_mr()
implicit_get_child_mr()
xa_cmpxchg()
atomic_dec_and_test(num_deferred_mr)
wait_event(imr->q_deferred_work)
ib_umem_odp_release(odp_imr)
kfree(odp_imr)
At this point in mlx5_ib_free_implicit_mr() the implicit_children list is
supposed to be empty forever so that destroy_unused_implicit_child_mr()
and related are not and will not be running.
Since it is not empty the destroy_unused_implicit_child_mr() flow ends up
touching deallocated memory as mlx5_ib_free_implicit_mr() already tore down the
imr parent.
The solution is to flush out the prefetch wq by driving num_deferred_work
to zero after creation of new prefetch work is blocked.
Fixes: 5256edcb98a1 ("RDMA/mlx5: Rework implicit ODP destroy")
Link: https://lore.kernel.org/r/20200719065435.130722-1-leon@xxxxxxxxxx
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/infiniband/hw/mlx5/odp.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/drivers/infiniband/hw/mlx5/odp.c b/drivers/infiniband/hw/mlx5/odp.c
index 3de7606d4a1a7..bdeb6500a9191 100644
--- a/drivers/infiniband/hw/mlx5/odp.c
+++ b/drivers/infiniband/hw/mlx5/odp.c
@@ -601,6 +601,23 @@ void mlx5_ib_free_implicit_mr(struct mlx5_ib_mr *imr)
*/
synchronize_srcu(&dev->odp_srcu);
+ /*
+ * All work on the prefetch list must be completed, xa_erase() prevented
+ * new work from being created.
+ */
+ wait_event(imr->q_deferred_work, !atomic_read(&imr->num_deferred_work));
+
+ /*
+ * At this point it is forbidden for any other thread to enter
+ * pagefault_mr() on this imr. It is already forbidden to call
+ * pagefault_mr() on an implicit child. Due to this additions to
+ * implicit_children are prevented.
+ */
+
+ /*
+ * Block destroy_unused_implicit_child_mr() from incrementing
+ * num_deferred_work.
+ */
xa_lock(&imr->implicit_children);
xa_for_each (&imr->implicit_children, idx, mtt) {
__xa_erase(&imr->implicit_children, idx);
@@ -609,9 +626,8 @@ void mlx5_ib_free_implicit_mr(struct mlx5_ib_mr *imr)
xa_unlock(&imr->implicit_children);
/*
- * 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.
+ * Wait for any concurrent destroy_unused_implicit_child_mr() to
+ * complete.
*/
wait_event(imr->q_deferred_work, !atomic_read(&imr->num_deferred_work));
--
2.25.1
