From aa116b810ac9077a263ed8679fb4d595f180e0eb Mon Sep 17 00:00:00 2001 From: Jason Gunthorpe Date: Tue, 1 Oct 2019 12:38:19 -0300 Subject: [PATCH] RDMA/mlx5: Order num_pending_prefetch properly with synchronize_srcu During destroy setting live = 0 and then synchronize_srcu() prevents num_pending_prefetch from incrementing, and also, ensures that all work holding that count is queued on the WQ. Testing before causes races of the form: CPU0 CPU1 dereg_mr() mlx5_ib_advise_mr_prefetch() srcu_read_lock() num_pending_prefetch_inc() if (!live) live = 0 atomic_read() == 0 // skip flush_workqueue() atomic_inc() queue_work(); srcu_read_unlock() WARN_ON(atomic_read()) // Fails Swap the order so that the synchronize_srcu() prevents this. Fixes: a6bc3875f176 ("IB/mlx5: Protect against prefetch of invalid MR") Link: https://lore.kernel.org/r/20191001153821.23621-5-jgg@ziepe.ca Reviewed-by: Artemy Kovalyov Signed-off-by: Jason Gunthorpe --- drivers/infiniband/hw/mlx5/mr.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c index e7f840f..0ee8fa0 100644 --- a/drivers/infiniband/hw/mlx5/mr.c +++ b/drivers/infiniband/hw/mlx5/mr.c @@ -1609,13 +1609,14 @@ static void dereg_mr(struct mlx5_ib_dev *dev, struct mlx5_ib_mr *mr) */ mr->live = 0; + /* Wait for all running page-fault handlers to finish. */ + synchronize_srcu(&dev->mr_srcu); + /* dequeue pending prefetch requests for the mr */ if (atomic_read(&mr->num_pending_prefetch)) flush_workqueue(system_unbound_wq); WARN_ON(atomic_read(&mr->num_pending_prefetch)); - /* Wait for all running page-fault handlers to finish. */ - synchronize_srcu(&dev->mr_srcu); /* Destroy all page mappings */ if (!umem_odp->is_implicit_odp) mlx5_ib_invalidate_range(umem_odp, -- 2.7.4