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@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
include/linux/page-flags.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
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;
}
--
2.45.2
