linux-kernel - Re: [Intel-wired-lan] [PATCH net-next v11 12/12] libeth: xdp: access ->pp through netmem

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Message-ID: <35592824-6749-4fa4-89d9-2de9caccc695@gmail.com>
Date: Fri, 18 Jul 2025 10:18:41 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Byungchul Park <byungchul@...com>, kernel test robot <lkp@...el.com>
Cc: willy@...radead.org, netdev@...r.kernel.org,
 oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
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Subject: Re: [Intel-wired-lan] [PATCH net-next v11 12/12] libeth: xdp: access
 ->pp through netmem_desc instead of page

On 7/18/25 02:14, Byungchul Park wrote:
...>>>
>>>     In file included from include/linux/container_of.h:5,
>>>                      from include/linux/list.h:5,
>>>                      from include/linux/timer.h:5,
>>>                      from include/linux/netdevice.h:24,
>>>                      from include/trace/events/xdp.h:8,
>>>                      from include/linux/bpf_trace.h:5,
>>>                      from include/net/libeth/xdp.h:7,
>>>                      from drivers/net/ethernet/intel/libeth/tx.c:6:
>>>     include/net/libeth/xdp.h: In function 'libeth_xdp_prepare_buff':
>>>>> include/net/libeth/xdp.h:1295:23: warning: passing argument 1 of 'page_pool_page_is_pp' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
>>>          pp_page_to_nmdesc(page)->pp->p.offset, len, true);
>>>                            ^~~~
>>>     include/linux/build_bug.h:30:63: note: in definition of macro 'BUILD_BUG_ON_INVALID'
>>>      #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
>>>                                                                    ^
>>>     include/net/netmem.h:301:2: note: in expansion of macro 'DEBUG_NET_WARN_ON_ONCE'
>>>       DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(p));  \
>>>       ^~~~~~~~~~~~~~~~~~~~~~
>>>     include/net/libeth/xdp.h:1295:5: note: in expansion of macro 'pp_page_to_nmdesc'
>>>          pp_page_to_nmdesc(page)->pp->p.offset, len, true);
>>>          ^~~~~~~~~~~~~~~~~
>>>     In file included from arch/arm/include/asm/cacheflush.h:10,
>>>                      from include/linux/cacheflush.h:5,
>>>                      from include/linux/highmem.h:8,
>>>                      from include/linux/bvec.h:10,
>>>                      from include/linux/skbuff.h:17,
>>>                      from include/net/net_namespace.h:43,
>>>                      from include/linux/netdevice.h:38,
>>>                      from include/trace/events/xdp.h:8,
>>>                      from include/linux/bpf_trace.h:5,
>>>                      from include/net/libeth/xdp.h:7,
>>>                      from drivers/net/ethernet/intel/libeth/tx.c:6:
>>>     include/linux/mm.h:4176:54: note: expected 'struct page *' but argument is of type 'const struct page *'
>>>      static inline bool page_pool_page_is_pp(struct page *page)
>>>                                              ~~~~~~~~~~~~~^~~~
>>
>> Oh.  page_pool_page_is_pp() in the mainline code already has this issue
>> that the helper cannot take const struct page * as argument.

Probably not, and probably for wrong reasons. netmem_ref is define
as an integer, compilers cast away such const unlike const pointers.

>> How should we resolve the issue?  Changing page_pool_page_is_pp() to
>> macro and using _Generic again looks too much.  Or should we?  Any idea?

page_pool_page_is_pp() doesn't change the page, just make the
argument const.

bool page_pool_page_is_pp(const struct page *page)

-- 
Pavel Begunkov