src/patches/suse-2.6.27.25/patches.xen/849-sfc-tx-skb-lock.patch

   1 From: http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/3a4410c4504e
   2 # HG changeset 849 patch
   3 # User Keir Fraser <keir.fraser@citrix.com>
   4 # Date 1238497253 -3600
   5 # Node ID 3a4410c4504ea64f2c1e873df3234938366050ad
   6 # Parent  ab1d4fbbe4bf93f203e0c4d62c18bd248e4f1d4a
   7 Subject: sfc_netfront: Only clear tx_skb when ready for netif_wake_queue
   8 (doing otherwise could result in a lost packet) and document use of
   9 locks to protect tx_skb
  10 References: bnc#489721
  11 Patch-mainline: obsolete
  12
  13 Signed-off-by: Kieran Mansley <kmansley@solarflare.com>
  14 Acked-by: jbeulich@novell.com
  15
  16 --- sle11-2009-04-09.orig/drivers/xen/sfc_netfront/accel.h      2009-04-09 14:23:18.000000000 +0200
  17 +++ sle11-2009-04-09/drivers/xen/sfc_netfront/accel.h   2009-04-09 14:41:38.000000000 +0200
  18 @@ -261,8 +261,10 @@ typedef struct netfront_accel_vnic {
  19
  20         int poll_enabled;
  21
  22 -       /** A spare slot for a TX packet.  This is treated as an extension
  23 -        * of the DMA queue. */
  24 +       /** A spare slot for a TX packet.  This is treated as an
  25 +        * extension of the DMA queue.  Reads require either
  26 +        * netfront's tx_lock or the vnic tx_lock; writes require both
  27 +        * locks */
  28         struct sk_buff *tx_skb;
  29
  30         /** Keep track of fragments of SSR packets */
  31 --- sle11-2009-04-09.orig/drivers/xen/sfc_netfront/accel_netfront.c     2009-03-30 16:16:28.000000000 +0200
  32 +++ sle11-2009-04-09/drivers/xen/sfc_netfront/accel_netfront.c  2009-04-09 14:42:13.000000000 +0200
  33 @@ -65,7 +65,7 @@ static int netfront_accel_netdev_start_x
  34                 BUG_ON(vnic->net_dev != net_dev);
  35                 DPRINTK("%s stopping queue\n", __FUNCTION__);
  36
  37 -               /* Netfront's lock protects tx_skb */
  38 +               /* Need netfront's tx_lock and vnic tx_lock to write tx_skb */
  39                 spin_lock_irqsave(&np->tx_lock, flags2);
  40                 BUG_ON(vnic->tx_skb != NULL);
  41                 vnic->tx_skb = skb;
  42 @@ -183,7 +183,7 @@ static int netfront_accel_check_ready(st
  43
  44         BUG_ON(vnic == NULL);
  45
  46 -       /* This is protected by netfront's lock */
  47 +       /* Read of tx_skb is protected by netfront's tx_lock */
  48         return vnic->tx_skb == NULL;
  49  }
  50
  51 --- sle11-2009-04-09.orig/drivers/xen/sfc_netfront/accel_vi.c   2009-04-09 14:23:18.000000000 +0200
  52 +++ sle11-2009-04-09/drivers/xen/sfc_netfront/accel_vi.c        2009-04-09 14:41:38.000000000 +0200
  53 @@ -980,39 +980,35 @@ static void netfront_accel_vi_not_busy(n
  54  {
  55         struct netfront_info *np = ((struct netfront_info *)
  56                                     netdev_priv(vnic->net_dev));
  57 -       struct sk_buff *skb;
  58         int handled;
  59         unsigned long flags;
  60 -
  61 +
  62         /*
  63 -        * TODO if we could safely check tx_skb == NULL and return
  64 -        * early without taking the lock, that would obviously help
  65 -        * performance
  66 +        * We hold the vnic tx_lock which is sufficient to exclude
  67 +        * writes to tx_skb
  68          */
  69
  70 -       /* Take the netfront lock which protects tx_skb. */
  71 -       spin_lock_irqsave(&np->tx_lock, flags);
  72         if (vnic->tx_skb != NULL) {
  73                 DPRINTK("%s trying to send spare buffer\n", __FUNCTION__);
  74
  75 -               skb = vnic->tx_skb;
  76 -               vnic->tx_skb = NULL;
  77 -
  78 -               spin_unlock_irqrestore(&np->tx_lock, flags);
  79 -
  80 -               handled = netfront_accel_vi_tx_post(vnic, skb);
  81 +               handled = netfront_accel_vi_tx_post(vnic, vnic->tx_skb);
  82
  83 -               spin_lock_irqsave(&np->tx_lock, flags);
  84 -
  85                 if (handled != NETFRONT_ACCEL_STATUS_BUSY) {
  86                         DPRINTK("%s restarting tx\n", __FUNCTION__);
  87 +
  88 +                       /* Need netfront tx_lock and vnic tx_lock to
  89 +                        * write tx_skb */
  90 +                       spin_lock_irqsave(&np->tx_lock, flags);
  91 +
  92 +                       vnic->tx_skb = NULL;
  93 +
  94                         if (netfront_check_queue_ready(vnic->net_dev)) {
  95                                 netif_wake_queue(vnic->net_dev);
  96                                 NETFRONT_ACCEL_STATS_OP
  97                                         (vnic->stats.queue_wakes++);
  98                         }
  99 -               } else {
 100 -                       vnic->tx_skb = skb;
 101 +                       spin_unlock_irqrestore(&np->tx_lock, flags);
 102 +
 103                 }
 104
 105                 /*
 106 @@ -1021,7 +1017,6 @@ static void netfront_accel_vi_not_busy(n
 107                  */
 108                 BUG_ON(handled == NETFRONT_ACCEL_STATUS_CANT);
 109         }
 110 -       spin_unlock_irqrestore(&np->tx_lock, flags);
 111  }
 112
 113