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

[Helge Deller <deller@kernel.org>]

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;