netdev - Re: [PATCH v2 net-next] net: usb: smsc95xx: stop lying about skb->truesize

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Date: Thu, 9 May 2024 10:25:18 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: kernel test robot <lkp@...el.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, oe-kbuild-all@...ts.linux.dev, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Steve Glendinning <steve.glendinning@...well.net>, 
	UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH v2 net-next] net: usb: smsc95xx: stop lying about skb->truesize

On Thu, May 9, 2024 at 8:01 AM kernel test robot <lkp@...el.com> wrote:
>
> Hi Eric,
>
> kernel test robot noticed the following build warnings:
>
> [auto build test WARNING on net-next/main]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Eric-Dumazet/net-usb-smsc95xx-stop-lying-about-skb-truesize/20240508-155316
> base:   net-next/main
> patch link:    https://lore.kernel.org/r/20240508075159.1646031-1-edumazet%40google.com
> patch subject: [PATCH v2 net-next] net: usb: smsc95xx: stop lying about skb->truesize
> config: arc-randconfig-r132-20240509 (https://download.01.org/0day-ci/archive/20240509/202405091310.KvncIecx-lkp@intel.com/config)
> compiler: arceb-elf-gcc (GCC) 13.2.0
> reproduce: (https://download.01.org/0day-ci/archive/20240509/202405091310.KvncIecx-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202405091310.KvncIecx-lkp@intel.com/
>
> sparse warnings: (new ones prefixed by >>)
> >> drivers/net/usb/smsc95xx.c:1815:19: sparse: sparse: incorrect type in assignment (different base types) @@     expected restricted __wsum [usertype] csum @@     got unsigned short x @@
>    drivers/net/usb/smsc95xx.c:1815:19: sparse:     expected restricted __wsum [usertype] csum
>    drivers/net/usb/smsc95xx.c:1815:19: sparse:     got unsigned short x
>    drivers/net/usb/smsc95xx.c: note: in included file (through include/net/checksum.h, include/linux/skbuff.h, include/net/net_namespace.h, ...):
>    arch/arc/include/asm/checksum.h:27:26: sparse: sparse: restricted __wsum degrades to integer
>    arch/arc/include/asm/checksum.h:27:36: sparse: sparse: restricted __wsum degrades to integer
>    arch/arc/include/asm/checksum.h:29:11: sparse: sparse: bad assignment (-=) to restricted __wsum
>    arch/arc/include/asm/checksum.h:30:16: sparse: sparse: restricted __wsum degrades to integer
>    arch/arc/include/asm/checksum.h:30:18: sparse: sparse: incorrect type in return expression (different base types) @@     expected restricted __sum16 @@     got unsigned int @@
>    arch/arc/include/asm/checksum.h:30:18: sparse:     expected restricted __sum16
>    arch/arc/include/asm/checksum.h:30:18: sparse:     got unsigned int
>
> vim +1815 drivers/net/usb/smsc95xx.c
>
>   1810
>   1811  static void smsc95xx_rx_csum_offload(struct sk_buff *skb)
>   1812  {
>   1813          u16 *csum_ptr = (u16 *)(skb_tail_pointer(skb) - 2);
>   1814
> > 1815          skb->csum = get_unaligned(csum_ptr);
>   1816          skb->ip_summed = CHECKSUM_COMPLETE;
>   1817          skb_trim(skb, skb->len - 2); /* remove csum */
>   1818  }
>   1819
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki


Please note this is not a new warning. Prior to my change we had :

drivers/net/usb/smsc95xx.c:1813:19: warning: incorrect type in
assignment (different base types)
drivers/net/usb/smsc95xx.c:1813:19:    expected restricted __wsum
[usertype] csum
drivers/net/usb/smsc95xx.c:1813:19:    got unsigned short [usertype]

I will submit a v3, to _also_ fix the sparse warning.