Subject: [obsolete] mm-fix-the-theoretical-compound_lock-vs-prep_new_page-race.patch removed from -mm tree
To: oleg@xxxxxxxxxx,aarcange@xxxxxxxxxx,mm-commits@xxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Fri, 31 Jan 2014 12:34:58 -0800
The patch titled
Subject: mm: fix the theoretical compound_lock() vs prep_new_page() race
has been removed from the -mm tree. Its filename was
mm-fix-the-theoretical-compound_lock-vs-prep_new_page-race.patch
This patch was dropped because it is obsolete
------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: mm: fix the theoretical compound_lock() vs prep_new_page() race
get/put_page(thp_tail) paths do get_page_unless_zero(page_head) +
compound_lock(). In theory this page_head can be already freed and
reallocated as alloc_pages(__GFP_COMP, smaller_order). In this case
get_page_unless_zero() can succeed right after set_page_refcounted(), and
compound_lock() can race with the non-atomic __SetPageHead() in
prep_compound_page().
Perhaps we should rework the thp locking (under discussion), but until
then this patch moves set_page_refcounted() and adds wmb() to ensure that
page->_count != 0 comes as a last change.
I am not sure about other callers of set_page_refcounted(), but at first
glance they look fine to me.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff -puN mm/page_alloc.c~mm-fix-the-theoretical-compound_lock-vs-prep_new_page-race mm/page_alloc.c
--- a/mm/page_alloc.c~mm-fix-the-theoretical-compound_lock-vs-prep_new_page-race
+++ a/mm/page_alloc.c
@@ -890,8 +890,6 @@ static int prep_new_page(struct page *pa
}
set_page_private(page, 0);
- set_page_refcounted(page);
-
arch_alloc_page(page, order);
kernel_map_pages(page, 1 << order, 1);
@@ -901,6 +899,16 @@ static int prep_new_page(struct page *pa
if (order && (gfp_flags & __GFP_COMP))
prep_compound_page(page, order);
+ /*
+ * Make sure the caller of get_page_unless_zero() will see the
+ * fully initialized page. Say, to ensure that compound_lock()
+ * can't race with the non-atomic __SetPage*() above.
+ */
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ smp_wmb();
+#endif
+ set_page_refcounted(page);
+
return 0;
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
origin.patch
linux-next.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
