The patch titled Subject: mm: open-code PageTail in folio_flags() and const_folio_flags() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-open-code-pagetail-in-folio_flags-and-const_folio_flags.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: "Matthew Wilcox (Oracle)" willy@infradead.org Subject: mm: open-code PageTail in folio_flags() and const_folio_flags() Date: Mon, 25 Nov 2024 20:17:18 +0000

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: fae7d834c43c ("mm: add __dump_folio()") Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Cc: stable@vger.kernel.org Cc: Kees Cook kees@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/page-flags.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/include/linux/page-flags.h~mm-open-code-pagetail-in-folio_flags-and-const_folio_flags +++ a/include/linux/page-flags.h @@ -306,7 +306,7 @@ static const unsigned long *const_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 { 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; } _

Patches currently in -mm which might be from willy@infradead.org are

mm-open-code-pagetail-in-folio_flags-and-const_folio_flags.patch mm-open-code-page_folio-in-dump_page.patch mm-page_alloc-cache-page_zone-result-in-free_unref_page.patch mm-make-alloc_pages_mpol-static.patch mm-page_alloc-export-free_frozen_pages-instead-of-free_unref_page.patch mm-page_alloc-move-set_page_refcounted-to-callers-of-post_alloc_hook.patch mm-page_alloc-move-set_page_refcounted-to-callers-of-prep_new_page.patch mm-page_alloc-move-set_page_refcounted-to-callers-of-get_page_from_freelist.patch mm-page_alloc-move-set_page_refcounted-to-callers-of-__alloc_pages_cpuset_fallback.patch mm-page_alloc-move-set_page_refcounted-to-callers-of-__alloc_pages_may_oom.patch mm-page_alloc-move-set_page_refcounted-to-callers-of-__alloc_pages_direct_compact.patch mm-page_alloc-move-set_page_refcounted-to-callers-of-__alloc_pages_direct_reclaim.patch mm-page_alloc-move-set_page_refcounted-to-callers-of-__alloc_pages_slowpath.patch mm-page_alloc-move-set_page_refcounted-to-end-of-__alloc_pages.patch mm-page_alloc-add-__alloc_frozen_pages.patch mm-mempolicy-add-alloc_frozen_pages.patch slab-allocate-frozen-pages.patch