Commit 4de22b2a authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Andrew Morton
Browse files

mm: open-code PageTail in folio_flags() and const_folio_flags() 

It is unsafe to call PageTail() in dump_page() as page_is_fake_head() will
almost certainly return true when called on a head page that is copied to
the stack.  That will cause the VM_BUG_ON_PGFLAGS() in const_folio_flags()
to trigger when it shouldn't.  Fortunately, we don't need to call
PageTail() here; it's fine to have a pointer to a virtual alias of the
page's flag word rather than the real page's flag word.

Link: https://lkml.kernel.org/r/20241125201721.2963278-1-willy@infradead.org


Fixes: fae7d834 ("mm: add __dump_folio()")
Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Cc: Kees Cook <kees@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent d699440f

include/linux/page-flags.h

+2 −2
Original line number Diff line number Diff line
@@ -306,7 +306,7 @@ static const unsigned long *const_folio_flags(const struct folio *folio, 
{

	const struct page *page = &folio->page;



	VM_BUG_ON_PGFLAGS(PageTail(page), page);

	VM_BUG_ON_PGFLAGS(page->compound_head & 1, page);

	VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page);

	return &page[n].flags;

}
@@ -315,7 +315,7 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n) 
{

	struct page *page = &folio->page;



	VM_BUG_ON_PGFLAGS(PageTail(page), page);

	VM_BUG_ON_PGFLAGS(page->compound_head & 1, page);

	VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page);

	return &page[n].flags;

}