From: Artemy Kovalyov artemyko@mellanox.com
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@kernel.org Signed-off-by: Artemy Kovalyov artemyko@mellanox.com Reviewed-by: Jason Gunthorpe jgg@mellanox.com Signed-off-by: Leon Romanovsky leonro@mellanox.com Signed-off-by: Jason Gunthorpe jgg@mellanox.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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); }