From: Artemy Kovalyov <artemyko@xxxxxxxxxxxx>
commit de5ed007a03d71daaa505f5daa4d3666530c7090 upstream.
Following race may occur because of the call_srcu and the placement of
the synchronize_srcu vs the xa_erase.
CPU0 CPU1
mlx5_ib_free_implicit_mr: destroy_unused_implicit_child_mr:
xa_erase(odp_mkeys)
synchronize_srcu()
xa_lock(implicit_children)
if (still in xarray)
atomic_inc()
call_srcu()
xa_unlock(implicit_children)
xa_erase(implicit_children):
xa_lock(implicit_children)
__xa_erase()
xa_unlock(implicit_children)
flush_workqueue()
[..]
free_implicit_child_mr_rcu:
(via call_srcu)
queue_work()
WARN_ON(atomic_read())
[..]
free_implicit_child_mr_work:
(via wq)
free_implicit_child_mr()
mlx5_mr_cache_invalidate()
mlx5_ib_update_xlt() <-- UMR QP fail
atomic_dec()
The wait_event() solves the race because it blocks until
free_implicit_child_mr_work() completes.
Fixes: 5256edcb98a1 ("RDMA/mlx5: Rework implicit ODP destroy")
Link: https://lore.kernel.org/r/20200227113918.94432-1-leon@xxxxxxxxxx
Signed-off-by: Artemy Kovalyov <artemyko@xxxxxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/infiniband/hw/mlx5/mlx5_ib.h | 1 +
drivers/infiniband/hw/mlx5/odp.c | 17 +++++++----------
2 files changed, 8 insertions(+), 10 deletions(-)
--- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
@@ -629,6 +629,7 @@ struct mlx5_ib_mr {
/* For ODP and implicit */
atomic_t num_deferred_work;
+ wait_queue_head_t q_deferred_work;
struct xarray implicit_children;
union {
struct rcu_head rcu;
--- a/drivers/infiniband/hw/mlx5/odp.c
+++ b/drivers/infiniband/hw/mlx5/odp.c
@@ -197,7 +197,8 @@ static void free_implicit_child_mr(struc
mr->parent = NULL;
mlx5_mr_cache_free(mr->dev, mr);
ib_umem_odp_release(odp);
- atomic_dec(&imr->num_deferred_work);
+ if (atomic_dec_and_test(&imr->num_deferred_work))
+ wake_up(&imr->q_deferred_work);
}
static void free_implicit_child_mr_work(struct work_struct *work)
@@ -516,6 +517,7 @@ struct mlx5_ib_mr *mlx5_ib_alloc_implici
imr->umem = &umem_odp->umem;
imr->is_odp_implicit = true;
atomic_set(&imr->num_deferred_work, 0);
+ init_waitqueue_head(&imr->q_deferred_work);
xa_init(&imr->implicit_children);
err = mlx5_ib_update_xlt(imr, 0,
@@ -573,10 +575,7 @@ void mlx5_ib_free_implicit_mr(struct mlx
* 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));
- }
+ wait_event(imr->q_deferred_work, !atomic_read(&imr->num_deferred_work));
/*
* Fence the imr before we destroy the children. This allows us to
@@ -607,10 +606,7 @@ void mlx5_ib_fence_odp_mr(struct mlx5_ib
/* Wait for all running page-fault handlers to finish. */
synchronize_srcu(&mr->dev->odp_srcu);
- if (atomic_read(&mr->num_deferred_work)) {
- flush_workqueue(system_unbound_wq);
- WARN_ON(atomic_read(&mr->num_deferred_work));
- }
+ wait_event(mr->q_deferred_work, !atomic_read(&mr->num_deferred_work));
dma_fence_odp_mr(mr);
}
@@ -1682,7 +1678,8 @@ static void destroy_prefetch_work(struct
u32 i;
for (i = 0; i < work->num_sge; ++i)
- atomic_dec(&work->frags[i].mr->num_deferred_work);
+ if (atomic_dec_and_test(&work->frags[i].mr->num_deferred_work))
+ wake_up(&work->frags[i].mr->q_deferred_work);
kvfree(work);
}
