Andrew Morton wrote:
> On Mon, 5 Jan 2015 13:46:22 +0200 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> > The only caller is __free_one_page(). By the time we should have
> > page->flags to be cleared already:
> >
> > - for 0-order pages though PCP list:
> > free_hot_cold_page()
> > free_pages_prepare()
> > free_pages_check()
> > page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
> > <put the page to PCP list>
> >
> > free_pcppages_bulk()
> > page = <withdraw pages from PCP list>
> > __free_one_page(page)
> >
> > - for non-0-order pages:
> > __free_pages_ok()
> > free_pages_prepare()
> > free_pages_check()
> > page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
> > free_one_page()
> > __free_one_page()
> >
> > So there's no way PageCompound() will return true in __free_one_page().
> > Let's remove dead destroy_compound_page() and put assert for page->flags
> > there instead.
>
> Well. An alternative would be to fix up the call site so those
> useful-looking checks actually get to check things. Perhaps under
> CONFIG_DEBUG_VM.
Something like this?
>From 5fd481c1c521112e9cea407f5a2644c9f93d0e14 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Date: Thu, 8 Jan 2015 15:59:23 +0200
Subject: [PATCH] mm: more checks on free_pages_prepare() for tail pages
Apart form being dead, destroy_compound_page() did some potentially
useful checks. Let's re-introduce them in free_pages_prepare(), where
they can be acctually triggered.
compound_order() assert is already in free_pages_prepare(). We have few
checks for tail pages left.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 27 +++++++++++++++++++++++----
1 file changed, 23 insertions(+), 4 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 23b85d97f61c..53f1a617866b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -767,21 +767,40 @@ static void free_one_page(struct zone *zone,
spin_unlock(&zone->lock);
}
+static int free_tail_pages_check(struct page *head_page, struct page *page)
+{
+ if (!IS_ENABLED(CONFIG_DEBUG_VM))
+ return 0;
+ if (unlikely(!PageTail(page))) {
+ bad_page(page, "PageTail not set", 0);
+ return 1;
+ }
+ if (unlikely(page->first_page != head_page)) {
+ bad_page(page, "first_page not consistent", 0);
+ return 1;
+ }
+ return 0;
+}
+
static bool free_pages_prepare(struct page *page, unsigned int order)
{
- int i;
- int bad = 0;
+ bool compound = PageCompound(page);
+ int i, bad = 0;
VM_BUG_ON_PAGE(PageTail(page), page);
- VM_BUG_ON_PAGE(PageHead(page) && compound_order(page) != order, page);
+ VM_BUG_ON_PAGE(compound && compound_order(page) != order, page);
trace_mm_page_free(page, order);
kmemcheck_free_shadow(page, order);
if (PageAnon(page))
page->mapping = NULL;
- for (i = 0; i < (1 << order); i++)
+ bad += free_pages_check(page);
+ for (i = 1; i < (1 << order); i++) {
+ if (compound)
+ free_tail_pages_check(page, page + i);
bad += free_pages_check(page + i);
+ }
if (bad)
return false;
if (order)
--
2.1.4
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>