lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Wed, 15 Mar 2017 18:07:16 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [PATCH v2 net-next] mlx4: Better use of order-0 pages in RX path

On Wed, 2017-03-15 at 16:06 -0700, Alexei Starovoitov wrote:

> yes. and we have 'xdp_tx_full' counter for it that we monitor.
> When tx ring and mtu are sized properly, we don't expect to see it
> incrementing at all. This is something in our control. 'Our' means
> humans that setup the environment.
> 'cache empty' condition is something ephemeral. Packets will be dropped
> and we won't have any tools to address it. These packets are real
> people requests. Any drop needs to be categorized.
> Like there is 'rx_fifo_errors' counter that mlx4 reports when
> hw is dropping packets before they reach the driver. We see it
> incrementing depending on the traffic pattern though overall Mpps
> through the nic is not too high and this is something we
> actively investigating too.


This all looks nice, except that current mlx4 driver does not have a
counter of failed allocations.

You are asking me to keep some inexistent functionality.

Look in David net tree :

mlx4_en_refill_rx_buffers()
...
   if (mlx4_en_prepare_rx_desc(...))
      break;


So in case of memory pressure, mlx4 stops working and not a single
counter is incremented/reported.

So I guess your supervision was not really tested.

Just to show you what you are asking, here is a diff against latest
version.

You want to make sure a fresh page is there before calling XDP program.

Is it really what you want ?

 drivers/net/ethernet/mellanox/mlx4/en_rx.c |   38 +++++++++++++----------------
 1 file changed, 18 insertions(+), 20 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index cc41f2f145541b469b52e7014659d5fdbb7dac68..e5ef8999087b52705faf083c94cde439aab9e2b7 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
@@ -793,10 +793,24 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
                if (xdp_prog) {
                        struct xdp_buff xdp;
                        struct page *npage;
-                       dma_addr_t ndma, dma;
+                       dma_addr_t dma;
                        void *orig_data;
                        u32 act;
 
+                       /* Make sure we have one page ready to replace this one, per Alexei request */
+                       if (unlikely(!ring->page_cache.index)) {
+                               npage = mlx4_alloc_page(priv, ring,
+                                                       &ring->page_cache.buf[0].dma,
+                                                       numa_mem_id(),
+                                                       GFP_ATOMIC | __GFP_MEMALLOC);
+                               if (!npage) {
+                                       /* replace this by a new ring->rx_alloc_failed++
+                                        */
+                                       ring->xdp_drop++;
+                                       goto next;
+                               }
+                               ring->page_cache.buf[0].page = npage;
+                       }
                        dma = frags[0].dma + frags[0].page_offset;
                        dma_sync_single_for_cpu(priv->ddev, dma,
                                                priv->frag_info[0].frag_size,
@@ -820,29 +834,13 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
                        case XDP_PASS:
                                break;
                        case XDP_TX:
-                               /* Make sure we have one page ready to replace this one */
-                               npage = NULL;
-                               if (!ring->page_cache.index) {
-                                       npage = mlx4_alloc_page(priv, ring,
-                                                               &ndma, numa_mem_id(),
-                                                               GFP_ATOMIC | __GFP_MEMALLOC);
-                                       if (!npage) {
-                                               ring->xdp_drop++;
-                                               goto next;
-                                       }
-                               }
                                if (likely(!mlx4_en_xmit_frame(ring, frags, dev,
                                                        length, cq->ring,
                                                        &doorbell_pending))) {
-                                       if (ring->page_cache.index) {
-                                               u32 idx = --ring->page_cache.index;
+                                       u32 idx = --ring->page_cache.index;
 
-                                               frags[0].page = ring->page_cache.buf[idx].page;
-                                               frags[0].dma = ring->page_cache.buf[idx].dma;
-                                       } else {
-                                               frags[0].page = npage;
-                                               frags[0].dma = ndma;
-                                       }
+                                       frags[0].page = ring->page_cache.buf[idx].page;
+                                       frags[0].dma = ring->page_cache.buf[idx].dma;
                                        frags[0].page_offset = XDP_PACKET_HEADROOM;
                                        goto next;
                                }





Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux - Powered by OpenVZ