From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
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")
Reviewed-by: Artemy Kovalyov <artemyko@xxxxxxxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
---
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 e7f840f306e46a..0ee8fa01177fc9 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,
--
2.23.0
