Hi Jesper,

I love your patch! Perhaps something to improve:

[auto build test WARNING on bpf-next/master]

url:    
https://github.com/0day-ci/linux/commits/Jesper-Dangaard-Brouer/bpf-New-approach-for-BPF-MTU-handling-and-enforcement/20201007-000903
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
config: s390-randconfig-r026-20201006 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 
1127662c6dc2a276839c75a42238b11a3ad00f32)
reproduce (this is a W=1 build):
        wget 
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O 
~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install s390 cross compiling tool for clang build
        # apt-get install binutils-s390x-linux-gnu
        # 
https://github.com/0day-ci/linux/commit/2065cee7d6b74c8f1dabae4e4e15999a841e3349
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review 
Jesper-Dangaard-Brouer/bpf-New-approach-for-BPF-MTU-handling-and-enforcement/20201007-000903
        git checkout 2065cee7d6b74c8f1dabae4e4e15999a841e3349
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=s390 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <l...@intel.com>

All warnings (new ones prefixed by >>):

   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro 
'__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:119:21: note: expanded from macro '__swab32'
           ___constant_swab32(x) :                 \
                              ^
   include/uapi/linux/swab.h:20:12: note: expanded from macro 
'___constant_swab32'
           (((__u32)(x) & (__u32)0x0000ff00UL) <<  8) |            \
                     ^
   In file included from net/core/dev.c:89:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro 
'__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:119:21: note: expanded from macro '__swab32'
           ___constant_swab32(x) :                 \
                              ^
   include/uapi/linux/swab.h:21:12: note: expanded from macro 
'___constant_swab32'
           (((__u32)(x) & (__u32)0x00ff0000UL) >>  8) |            \
                     ^
   In file included from net/core/dev.c:89:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro 
'__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:119:21: note: expanded from macro '__swab32'
           ___constant_swab32(x) :                 \
                              ^
   include/uapi/linux/swab.h:22:12: note: expanded from macro 
'___constant_swab32'
           (((__u32)(x) & (__u32)0xff000000UL) >> 24)))
                     ^
   In file included from net/core/dev.c:89:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro 
'__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:120:12: note: expanded from macro '__swab32'
           __fswab32(x))
                     ^
   In file included from net/core/dev.c:89:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:501:33: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writeb(value, PCI_IOBASE + addr);
                               ~~~~~~~~~~ ^
   include/asm-generic/io.h:511:59: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
                                                         ~~~~~~~~~~ ^
   include/asm-generic/io.h:521:59: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
                                                         ~~~~~~~~~~ ^
   include/asm-generic/io.h:609:20: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsb(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:617:20: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsw(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:625:20: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsl(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:634:21: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesb(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
   include/asm-generic/io.h:643:21: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesw(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
   include/asm-generic/io.h:652:21: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesl(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
   net/core/dev.c:4068:7: warning: unused variable 'mtu_check' 
[-Wunused-variable]
           bool mtu_check = false;
                ^
>> net/core/dev.c:4176:1: warning: unused label 'drop' [-Wunused-label]
   drop:
   ^~~~~
   net/core/dev.c:4949:1: warning: unused function 'sch_handle_ingress' 
[-Wunused-function]
   sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int 
*ret,
   ^
   net/core/dev.c:5094:19: warning: unused function 'nf_ingress' 
[-Wunused-function]
   static inline int nf_ingress(struct sk_buff *skb, struct packet_type 
**pt_prev,
                     ^
   In file included from net/core/dev.c:71:
   In file included from include/linux/uaccess.h:6:
   In file included from include/linux/sched.h:14:
   In file included from include/linux/pid.h:5:
   In file included from include/linux/rculist.h:10:
   In file included from include/linux/list.h:9:
   In file included from include/linux/kernel.h:12:
   In file included from include/linux/bitops.h:29:
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
                           "oi     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
                           "ni     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
                           "oi     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
                           "ni     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
                           "oi     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
                           "ni     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
                           "oi     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
                           "ni     %0,%b1\n"
                           ^
   24 warnings and 14 errors generated.
--
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro 
'__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:119:21: note: expanded from macro '__swab32'
           ___constant_swab32(x) :                 \
                              ^
   include/uapi/linux/swab.h:20:12: note: expanded from macro 
'___constant_swab32'
           (((__u32)(x) & (__u32)0x0000ff00UL) <<  8) |            \
                     ^
   In file included from net/core/dev.c:89:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro 
'__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:119:21: note: expanded from macro '__swab32'
           ___constant_swab32(x) :                 \
                              ^
   include/uapi/linux/swab.h:21:12: note: expanded from macro 
'___constant_swab32'
           (((__u32)(x) & (__u32)0x00ff0000UL) >>  8) |            \
                     ^
   In file included from net/core/dev.c:89:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro 
'__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:119:21: note: expanded from macro '__swab32'
           ___constant_swab32(x) :                 \
                              ^
   include/uapi/linux/swab.h:22:12: note: expanded from macro 
'___constant_swab32'
           (((__u32)(x) & (__u32)0xff000000UL) >> 24)))
                     ^
   In file included from net/core/dev.c:89:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
                                                           ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro 
'__le32_to_cpu'
   #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
                                                             ^
   include/uapi/linux/swab.h:120:12: note: expanded from macro '__swab32'
           __fswab32(x))
                     ^
   In file included from net/core/dev.c:89:
   In file included from include/linux/if_ether.h:19:
   In file included from include/linux/skbuff.h:31:
   In file included from include/linux/dma-mapping.h:11:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:72:
   include/asm-generic/io.h:501:33: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writeb(value, PCI_IOBASE + addr);
                               ~~~~~~~~~~ ^
   include/asm-generic/io.h:511:59: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
                                                         ~~~~~~~~~~ ^
   include/asm-generic/io.h:521:59: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           __raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
                                                         ~~~~~~~~~~ ^
   include/asm-generic/io.h:609:20: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsb(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:617:20: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsw(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:625:20: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           readsl(PCI_IOBASE + addr, buffer, count);
                  ~~~~~~~~~~ ^
   include/asm-generic/io.h:634:21: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesb(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
   include/asm-generic/io.h:643:21: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesw(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
   include/asm-generic/io.h:652:21: warning: performing pointer arithmetic on a 
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
           writesl(PCI_IOBASE + addr, buffer, count);
                   ~~~~~~~~~~ ^
>> net/core/dev.c:4176:1: warning: unused label 'drop' [-Wunused-label]
   drop:
   ^~~~~
   net/core/dev.c:4068:7: warning: unused variable 'mtu_check' 
[-Wunused-variable]
           bool mtu_check = false;
                ^
   net/core/dev.c:4949:1: warning: unused function 'sch_handle_ingress' 
[-Wunused-function]
   sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int 
*ret,
   ^
   net/core/dev.c:5094:19: warning: unused function 'nf_ingress' 
[-Wunused-function]
   static inline int nf_ingress(struct sk_buff *skb, struct packet_type 
**pt_prev,
                     ^
   In file included from net/core/dev.c:71:
   In file included from include/linux/uaccess.h:6:
   In file included from include/linux/sched.h:14:
   In file included from include/linux/pid.h:5:
   In file included from include/linux/rculist.h:10:
   In file included from include/linux/list.h:9:
   In file included from include/linux/kernel.h:12:
   In file included from include/linux/bitops.h:29:
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
                           "oi     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
                           "ni     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
                           "oi     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
                           "ni     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
                           "oi     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
                           "ni     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
                           "oi     %0,%b1\n"
                           ^
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
   arch/s390/include/asm/bitops.h:69:4: error: invalid operand in inline asm: 
'oi       $0,${1:b}'
   arch/s390/include/asm/bitops.h:90:4: error: invalid operand in inline asm: 
'ni       $0,${1:b}'
                           "ni     %0,%b1\n"
                           ^
   24 warnings and 14 errors generated.

vim +/drop +4176 net/core/dev.c

  4037  
  4038  /**
  4039   *      __dev_queue_xmit - transmit a buffer
  4040   *      @skb: buffer to transmit
  4041   *      @sb_dev: suboordinate device used for L2 forwarding offload
  4042   *
  4043   *      Queue a buffer for transmission to a network device. The caller 
must
  4044   *      have set the device and priority and built the buffer before 
calling
  4045   *      this function. The function can be called from an interrupt.
  4046   *
  4047   *      A negative errno code is returned on a failure. A success does 
not
  4048   *      guarantee the frame will be transmitted as it may be dropped due
  4049   *      to congestion or traffic shaping.
  4050   *
  4051   * 
-----------------------------------------------------------------------------------
  4052   *      I notice this method can also return errors from the queue 
disciplines,
  4053   *      including NET_XMIT_DROP, which is a positive value.  So, errors 
can also
  4054   *      be positive.
  4055   *
  4056   *      Regardless of the return value, the skb is consumed, so it is 
currently
  4057   *      difficult to retry a send to this method.  (You can bump the 
ref count
  4058   *      before sending to hold a reference for retry if you are 
careful.)
  4059   *
  4060   *      When calling this method, interrupts MUST be enabled.  This is 
because
  4061   *      the BH enable code must have IRQs enabled so that it will not 
deadlock.
  4062   *          --BLG
  4063   */
  4064  static int __dev_queue_xmit(struct sk_buff *skb, struct net_device 
*sb_dev)
  4065  {
  4066          struct net_device *dev = skb->dev;
  4067          struct netdev_queue *txq;
  4068          bool mtu_check = false;
  4069          bool again = false;
  4070          struct Qdisc *q;
  4071          int rc = -ENOMEM;
  4072  
  4073          skb_reset_mac_header(skb);
  4074  
  4075          if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP))
  4076                  __skb_tstamp_tx(skb, NULL, skb->sk, SCM_TSTAMP_SCHED);
  4077  
  4078          /* Disable soft irqs for various locks below. Also
  4079           * stops preemption for RCU.
  4080           */
  4081          rcu_read_lock_bh();
  4082  
  4083          skb_update_prio(skb);
  4084  
  4085          qdisc_pkt_len_init(skb);
  4086  #ifdef CONFIG_NET_CLS_ACT
  4087          mtu_check = skb_is_redirected(skb);
  4088          skb->tc_at_ingress = 0;
  4089  # ifdef CONFIG_NET_EGRESS
  4090          if (static_branch_unlikely(&egress_needed_key)) {
  4091                  unsigned int len_orig = skb->len;
  4092  
  4093                  skb = sch_handle_egress(skb, &rc, dev);
  4094                  if (!skb)
  4095                          goto out;
  4096                  /* BPF-prog ran and could have changed packet size 
beyond MTU */
  4097                  if (rc == NET_XMIT_SUCCESS && skb->len > len_orig)
  4098                          mtu_check = true;
  4099          }
  4100  # endif
  4101          /* MTU-check only happens on "last" net_device in a redirect 
sequence
  4102           * (e.g. above sch_handle_egress can steal SKB and 
skb_do_redirect it
  4103           * either ingress or egress to another device).
  4104           */
  4105          if (mtu_check && !is_skb_forwardable(dev, skb)) {
  4106                  rc = -EMSGSIZE;
  4107                  goto drop;
  4108          }
  4109  #endif
  4110          /* If device/qdisc don't need skb->dst, release it right now 
while
  4111           * its hot in this cpu cache.
  4112           */
  4113          if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
  4114                  skb_dst_drop(skb);
  4115          else
  4116                  skb_dst_force(skb);
  4117  
  4118          txq = netdev_core_pick_tx(dev, skb, sb_dev);
  4119          q = rcu_dereference_bh(txq->qdisc);
  4120  
  4121          trace_net_dev_queue(skb);
  4122          if (q->enqueue) {
  4123                  rc = __dev_xmit_skb(skb, q, dev, txq);
  4124                  goto out;
  4125          }
  4126  
  4127          /* The device has no queue. Common case for software devices:
  4128           * loopback, all the sorts of tunnels...
  4129  
  4130           * Really, it is unlikely that netif_tx_lock protection is 
necessary
  4131           * here.  (f.e. loopback and IP tunnels are clean ignoring 
statistics
  4132           * counters.)
  4133           * However, it is possible, that they rely on protection
  4134           * made by us here.
  4135  
  4136           * Check this and shot the lock. It is not prone from deadlocks.
  4137           *Either shot noqueue qdisc, it is even simpler 8)
  4138           */
  4139          if (dev->flags & IFF_UP) {
  4140                  int cpu = smp_processor_id(); /* ok because BHs are off 
*/
  4141  
  4142                  if (txq->xmit_lock_owner != cpu) {
  4143                          if (dev_xmit_recursion())
  4144                                  goto recursion_alert;
  4145  
  4146                          skb = validate_xmit_skb(skb, dev, &again);
  4147                          if (!skb)
  4148                                  goto out;
  4149  
  4150                          HARD_TX_LOCK(dev, txq, cpu);
  4151  
  4152                          if (!netif_xmit_stopped(txq)) {
  4153                                  dev_xmit_recursion_inc();
  4154                                  skb = dev_hard_start_xmit(skb, dev, 
txq, &rc);
  4155                                  dev_xmit_recursion_dec();
  4156                                  if (dev_xmit_complete(rc)) {
  4157                                          HARD_TX_UNLOCK(dev, txq);
  4158                                          goto out;
  4159                                  }
  4160                          }
  4161                          HARD_TX_UNLOCK(dev, txq);
  4162                          net_crit_ratelimited("Virtual device %s asks to 
queue packet!\n",
  4163                                               dev->name);
  4164                  } else {
  4165                          /* Recursion is detected! It is possible,
  4166                           * unfortunately
  4167                           */
  4168  recursion_alert:
  4169                          net_crit_ratelimited("Dead loop on virtual 
device %s, fix it urgently!\n",
  4170                                               dev->name);
  4171                  }
  4172          }
  4173  
  4174          rc = -ENETDOWN;
  4175          rcu_read_unlock_bh();
> 4176  drop:
  4177          atomic_long_inc(&dev->tx_dropped);
  4178          kfree_skb_list(skb);
  4179          return rc;
  4180  out:
  4181          rcu_read_unlock_bh();
  4182          return rc;
  4183  }
  4184  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-...@lists.01.org

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