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/mm-open-code-pagetail-in-folio_flags-and-const_folio_flags.patch
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@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx
Fixes: fae7d834c43c ("mm: add __dump_folio()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Kees Cook <kees@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxx 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
