Re: [PATCH] Fix 32-bit boot failure due inaccurate page_pool_page_is_pp()

[Byungchul Park <byungchul@sk.com>]

On Fri, Sep 12, 2025 at 05:49:15PM +0200, David Hildenbrand wrote:
> On 12.09.25 17:04, Helge Deller wrote:
> > Commit ee62ce7a1d90 ("page_pool: Track DMA-mapped pages and unmap them when
> > destroying the pool") changed PP_MAGIC_MASK from 0xFFFFFFFC to 0xc000007c on
> > 32-bit platforms.
> > 
> > The function page_pool_page_is_pp() uses PP_MAGIC_MASK to identify page pool
> > pages, but the remaining bits are not sufficient to unambiguously identify
> > such pages any longer.
> > 
> > So page_pool_page_is_pp() now sometimes wrongly reports pages as page pool
> > pages and as such triggers a kernel BUG as it believes it found a page pool
> > leak.
> > 
> > There are patches upcoming where page_pool_page_is_pp() will not depend on
> > PP_MAGIC_MASK and instead use page flags to identify page pool pages. Until
> > those patches are merged, the easiest temporary fix is to disable the check
> > on 32-bit platforms.
> > 
> > Cc: David Hildenbrand <david@redhat.com>
> > Cc: Toke Høiland-Jørgensen <toke@redhat.com>
> > Cc: Linux Memory Management List <linux-mm@kvack.org>
> > Cc: Linux parisc List <linux-parisc@vger.kernel.org>
> > Cc: <stable@vger.kernel.org> # v6.15+
> > Signed-off-by: Helge Deller <deller@gmx.de>
> > Link: https://www.spinics.net/lists/kernel/msg5849623.html
> > Fixes: ee62ce7a1d90 ("page_pool: Track DMA-mapped pages and unmap them when destroying the pool")
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 1ae97a0b8ec7..f3822ae70a81 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -4190,7 +4190,7 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
> >    */
> >   #define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL)
> > 
> > -#ifdef CONFIG_PAGE_POOL
> > +#if defined(CONFIG_PAGE_POOL) && defined(CONFIG_64BIT)
> >   static inline bool page_pool_page_is_pp(const struct page *page)
> >   {
> >       treturn (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
> > 
> 
> As a temporary fix this LGTM.

Sure.  As a temporary fix, why not.

I need to start the work replacing page_pool_page_is_pp() with using
page type again tho.

	Byungchul

> But I want to hear other opinions.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> 
> --
> Cheers
> 
> David / dhildenb
>