IB/mlx5: Fix implicit MR GC

When implicit MR's leaf MKey becomes unused, i.e. when it's
last page being released my MMU invalidation it is marked as "dying"
and scheduled for release by garbage collector.
Currentle consequent page fault may remove "dying" flag.
Treat leaf MKey as non-existent once it was scheduled to removal
by GC.

Fixes: 81713d3788 ('IB/mlx5: Add implicit MR support')
Signed-off-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/odp.c

@@ -57,7 +57,7 @@ static int check_parent(struct ib_umem_odp *odp,
 {
 	struct mlx5_ib_mr *mr = odp->private;
 
-	return mr && mr->parent == parent;
+	return mr && mr->parent == parent && !odp->dying;
 }
 
 static struct ib_umem_odp *odp_next(struct ib_umem_odp *odp)
@@ -158,13 +158,6 @@ static void mr_leaf_free_action(struct work_struct *work)
 	mr->parent = NULL;
 	synchronize_srcu(&mr->dev->mr_srcu);
 
-	if (!READ_ONCE(odp->dying)) {
-		mr->parent = imr;
-		if (atomic_dec_and_test(&imr->num_leaf_free))
-			wake_up(&imr->q_leaf_free);
-		return;
-	}
-
 	ib_umem_release(odp->umem);
 	if (imr->live)
 		mlx5_ib_update_xlt(imr, idx, 1, 0,
@@ -436,8 +429,6 @@ next_mr:
 		nentries++;
 	}
 
-	odp->dying = 0;
-
 	/* Return first odp if region not covered by single one */
 	if (likely(!result))
 		result = odp;