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

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Message-ID: <20250721010313.GA21807@system.software.com>
Date: Mon, 21 Jul 2025 10:03:13 +0900
From: Byungchul Park <byungchul@...com>
To: Pavel Begunkov <asml.silence@...il.com>
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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 Fri, Jul 18, 2025 at 10:32:38AM +0100, Pavel Begunkov wrote:
> On 7/18/25 10:18, Pavel Begunkov wrote:
> > On 7/18/25 02:14, Byungchul Park wrote:
> ...>>>>     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.
> 
> Taking a look libeth, at least at the reported spot it does
> page->pp->p.offset, that should be fine. And your problem
> is caused by the is_pp check in pp_page_to_nmdesc().

Exactly, but you asked me to add the check,
DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(p)) in pp_page_to_nmdesc().

What I meant was, in order to apply that, page_pool_page_is_pp() should
take 'const struct page *' as argument.

I think it's good idea to change the proto type like, as you said:

   static inline bool page_pool_page_is_pp(const struct page *page);

Thanks.

	Byungchul
> 
> --
> Pavel Begunkov
>