排查 “Detected Tx Unit Hang”问题

实现功能：

使用自己已经分配的内存让skb->data指向，而不是使用alloc_malloc()。

部分代码如下：

             /*
              * build a new sk_buff
              */
             //struct sk_buff *send_skb = kmem_cache_alloc_node(skbuff_head_cache, GFP_ATOMIC & ~__GFP_DMA, NUMA_NO_NODE);
             struct sk_buff *send_skb = kmem_cache_alloc(skbuff_head_cache, GFP_ATOMIC & ~__GFP_DMA);

             if (!send_skb) {
                 //spin_unlock(&lock);
                 return NF_DROP;
             }

             //printk("what2\n");
             memset(send_skb, , offsetof(struct sk_buff, tail));
             atomic_set(&send_skb->users, );
             send_skb->cloned = ;

             send_skb->head = mmap_buf + ;
             send_skb->data = mmap_buf + ;
             

第18行，mmap_buf是提前分配的内存。

在/var/log/messages中网卡驱动会输出错误信息：

 ep  :: 10g-host2 kernel: ixgbe ::00.0: eth2: Detected Tx Unit Hang
 Sep  :: 10g-host2 kernel:  Tx Queue             <>
 Sep  :: 10g-host2 kernel:  TDH, TDT             <>, <1ea>
 Sep  :: 10g-host2 kernel:  next_to_use          <1ea>
 Sep  :: 10g-host2 kernel:  next_to_clean        <>
 Sep  :: 10g-host2 kernel: ixgbe ::00.0: eth2: Detected Tx Unit Hang
 Sep  :: 10g-host2 kernel:  Tx Queue             <>
 Sep  :: 10g-host2 kernel:  TDH, TDT             <>, <1eb>
 Sep  :: 10g-host2 kernel:  next_to_use          <1eb>
 Sep  :: 10g-host2 kernel:  next_to_clean        <>
 Sep  :: 10g-host2 kernel: ixgbe ::00.0: eth2: Detected Tx Unit Hang
 Sep  :: 10g-host2 kernel:  Tx Queue             <>
 Sep  :: 10g-host2 kernel:  TDH, TDT             <>, <1ea>
 Sep  :: 10g-host2 kernel:  next_to_use          <1ea>
 Sep  :: 10g-host2 kernel:  next_to_clean        <>
 Sep  :: 10g-host2 kernel: ixgbe ::00.0: eth2: Detected Tx Unit Hang
 Sep  :: 10g-host2 kernel:  Tx Queue             <>
 Sep  :: 10g-host2 kernel:  TDH, TDT             <>, <1ea>
 Sep  :: 10g-host2 kernel:  next_to_use          <1ea>
 Sep  :: 10g-host2 kernel:  next_to_clean        <>
 Sep  :: 10g-host2 kernel: ixgbe ::00.0: eth2: Detected Tx Unit Hang
 Sep  :: 10g-host2 kernel:  Tx Queue             <>
 Sep  :: 10g-host2 kernel:  TDH, TDT             <>, <1ef>
 Sep  :: 10g-host2 kernel:  next_to_use          <1ef>
 Sep  :: 10g-host2 kernel:  next_to_clean        <>
 Sep  :: 10g-host2 kernel: ixgbe ::00.0: eth2: Detected Tx Unit Hang
 Sep  :: 10g-host2 kernel:  Tx Queue             <>
 Sep  :: 10g-host2 kernel:  TDH, TDT             <>, <1ec>
 Sep  :: 10g-host2 kernel:  next_to_use          <1ec>
 Sep  :: 10g-host2 kernel:  next_to_clean        <>
 Sep  :: 10g-host2 kernel: ixgbe ::00.0: eth2: Detected Tx Unit Hang

在排除各种原因后，定位为分配的mmap_buf存在问题。使用vmalloc()分配不正确，改为kmalloc()后正常。

《Linux内核设计与实现》第12.5节有解释，应该是：网卡设备要求分配的物理地址连续，而vmalloc()只是虚拟地址连续