Re: [PATCH v6 net-next 4/9] vhost-net: allow configuring extended features

[Paolo Abeni <pabeni@redhat.com>]

On 6/27/25 2:18 PM, Michael S. Tsirkin wrote:
> On Fri, Jun 27, 2025 at 12:28:00PM +0200, Paolo Abeni wrote:
>> On 6/27/25 8:41 AM, kernel test robot wrote:
>>> 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/Paolo-Abeni/scripts-kernel_doc-py-properly-handle-VIRTIO_DECLARE_FEATURES/20250624-221751
>>> base:   net-next/main
>>> patch link:    https://lore.kernel.org/r/23e46bff5333015d92bf0876033750d9fbf555a0.1750753211.git.pabeni%40redhat.com
>>> patch subject: [PATCH v6 net-next 4/9] vhost-net: allow configuring extended features
>>> config: csky-randconfig-001-20250627 (https://download.01.org/0day-ci/archive/20250627/202506271443.G9cAx8PS-lkp@intel.com/config)
>>> compiler: csky-linux-gcc (GCC) 15.1.0
>>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250627/202506271443.G9cAx8PS-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@intel.com>
>>> | Closes: https://lore.kernel.org/oe-kbuild-all/202506271443.G9cAx8PS-lkp@intel.com/
>>>
>>> All warnings (new ones prefixed by >>):
>>>
>>>    In file included from include/linux/uaccess.h:12,
>>>                     from include/linux/sched/task.h:13,
>>>                     from include/linux/sched/signal.h:9,
>>>                     from include/linux/rcuwait.h:6,
>>>                     from include/linux/percpu-rwsem.h:7,
>>>                     from include/linux/fs.h:34,
>>>                     from include/linux/compat.h:17,
>>>                     from drivers/vhost/net.c:8:
>>>    arch/csky/include/asm/uaccess.h: In function '__get_user_fn.constprop':
>>>>> arch/csky/include/asm/uaccess.h:147:9: warning: 'retval' is used uninitialized [-Wuninitialized]
>>>      147 |         __asm__ __volatile__(                           \
>>>          |         ^~~~~~~
>>>    arch/csky/include/asm/uaccess.h:187:17: note: in expansion of macro '__get_user_asm_64'
>>>      187 |                 __get_user_asm_64(x, ptr, retval);
>>>          |                 ^~~~~~~~~~~~~~~~~
>>>    arch/csky/include/asm/uaccess.h:170:13: note: 'retval' was declared here
>>>      170 |         int retval;
>>>          |             ^~~~~~
>>>
>>>
>>> vim +/retval +147 arch/csky/include/asm/uaccess.h
>>>
>>> da551281947cb2c Guo Ren 2018-09-05  141  
>>> e58a41c2226847f Guo Ren 2021-04-21  142  #define __get_user_asm_64(x, ptr, err)			\
>>> da551281947cb2c Guo Ren 2018-09-05  143  do {							\
>>> da551281947cb2c Guo Ren 2018-09-05  144  	int tmp;					\
>>> e58a41c2226847f Guo Ren 2021-04-21  145  	int errcode;					\
>>> e58a41c2226847f Guo Ren 2021-04-21  146  							\
>>> e58a41c2226847f Guo Ren 2021-04-21 @147  	__asm__ __volatile__(				\
>>> e58a41c2226847f Guo Ren 2021-04-21  148  	"1:   ldw     %3, (%2, 0)     \n"		\
>>> da551281947cb2c Guo Ren 2018-09-05  149  	"     stw     %3, (%1, 0)     \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  150  	"2:   ldw     %3, (%2, 4)     \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  151  	"     stw     %3, (%1, 4)     \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  152  	"     br      4f              \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  153  	"3:   mov     %0, %4          \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  154  	"     br      4f              \n"		\
>>> da551281947cb2c Guo Ren 2018-09-05  155  	".section __ex_table, \"a\"   \n"		\
>>> da551281947cb2c Guo Ren 2018-09-05  156  	".align   2                   \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  157  	".long    1b, 3b              \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  158  	".long    2b, 3b              \n"		\
>>> da551281947cb2c Guo Ren 2018-09-05  159  	".previous                    \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  160  	"4:                           \n"		\
>>> e58a41c2226847f Guo Ren 2021-04-21  161  	: "=r"(err), "=r"(x), "=r"(ptr),		\
>>> e58a41c2226847f Guo Ren 2021-04-21  162  	  "=r"(tmp), "=r"(errcode)			\
>>> e58a41c2226847f Guo Ren 2021-04-21  163  	: "0"(err), "1"(x), "2"(ptr), "3"(0),		\
>>> e58a41c2226847f Guo Ren 2021-04-21  164  	  "4"(-EFAULT)					\
>>> da551281947cb2c Guo Ren 2018-09-05  165  	: "memory");					\
>>> da551281947cb2c Guo Ren 2018-09-05  166  } while (0)
>>> da551281947cb2c Guo Ren 2018-09-05  167  
>>
>> AFAICS the issue reported here is in the arch-specific uaccess helpers
>> and not related to this series.
>>
>> /P
> 
> I think it's due to code like this in your patch:
> 
> +                       if (get_user(features, featurep + 1 + i))
> +                               return -EFAULT;
> 
> the specific arch might have a bug that this is unconvering,
> or a limitation, I can't say.
> 
> Seems worth fixing, though.
> 
> Poke the mainatiners?

FTR, I tried the boot reproducer locally, and does not trigger here.

The above statement is AFAICS legit, and the issue, if any, is present
into such arch. I would not say this patch is 'uncovering' anything, as
the relevant pattern is very common.

Possibly the test robot added support for csky only recently?

I will ping the arch maintainers, but I suggest/argue not blocking this
series for this thing.

Thanks,

Paolo