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 --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; }