Messages in this thread Patch in this message | | | Subject | Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before prod db updating | From | Saeed Mahameed <> | Date | Fri, 12 Jan 2018 11:53:22 -0800 |
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On 01/12/2018 08:46 AM, Eric Dumazet wrote: > On Fri, 2018-01-12 at 09:32 -0700, Jason Gunthorpe wrote: >> On Fri, Jan 12, 2018 at 11:42:22AM +0800, Jianchao Wang wrote: >>> Customer reported memory corruption issue on previous mlx4_en driver >>> version where the order-3 pages and multiple page reference counting >>> were still used. >>> >>> Finally, find out one of the root causes is that the HW may see stale >>> rx_descs due to prod db updating reaches HW before rx_desc. Especially >>> when cross order-3 pages boundary and update a new one, HW may write >>> on the pages which may has been freed and allocated again by others. >>> >>> To fix it, add a wmb between rx_desc and prod db updating to ensure >>> the order. Even thougth order-0 and page recycling has been introduced, >>> the disorder between rx_desc and prod db still could lead to corruption >>> on different inbound packages. >>> >>> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com> >>> drivers/net/ethernet/mellanox/mlx4/en_rx.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c >>> index 85e28ef..eefa82c 100644 >>> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c >>> @@ -555,7 +555,7 @@ static void mlx4_en_refill_rx_buffers(struct mlx4_en_priv *priv, >>> break; >>> ring->prod++; >>> } while (likely(--missing)); >>> - >>> + wmb(); /* ensure rx_desc updating reaches HW before prod db updating */ >>> mlx4_en_update_rx_prod_db(ring); >>> } >>> >> >> Does this need to be dma_wmb(), and should it be in >> mlx4_en_update_rx_prod_db ? >> > > +1 on dma_wmb() > > On what architecture bug was observed ? > > In any case, the barrier should be moved in mlx4_en_update_rx_prod_db() > I think. >
+1 on dma_wmb(), thanks Eric for reviewing this.
The barrier is also needed elsewhere in the code as well, but I wouldn't put it in mlx4_en_update_rx_prod_db(), just to allow batch filling of all rx rings and then hit the barrier only once. As a rule of thumb, mem barriers are the ring API caller responsibility.
e.g. in mlx4_en_activate_rx_rings(): between mlx4_en_fill_rx_buffers(priv); and the loop that updates rx prod for all rings ring, the dma_wmb is needed, see below.
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c index b4d144e67514..65541721a240 100644 --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c @@ -370,6 +370,8 @@ int mlx4_en_activate_rx_rings(struct mlx4_en_priv *priv) if (err) goto err_buffers;
+ dma_wmb(); + for (ring_ind = 0; ring_ind < priv->rx_ring_num; ring_ind++) { ring = priv->rx_ring[ring_ind];
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