diff mbox series

[1/2] mm: Open-code PageTail in folio_flags() and const_folio_flags()

Message ID 20241125201721.2963278-1-willy@infradead.org (mailing list archive)
State New
Headers show
Series [1/2] mm: Open-code PageTail in folio_flags() and const_folio_flags() | expand

Commit Message

Matthew Wilcox (Oracle) Nov. 25, 2024, 8:17 p.m. UTC 
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.

Fixes: fae7d834c43c (mm: add __dump_folio())
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: stable@vger.kernel.org
---
 include/linux/page-flags.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 2220bfec278e..cf46ac720802 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -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;
 }