From 5eaf1a9e233d61438377f57facb167f8208ba9fd Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 21 Jan 2014 15:49:04 -0800
Subject: mm: thp: turn compound_head() into BUG_ON(!PageTail) in
get_huge_page_tail()
get_huge_page_tail()->compound_head() looks confusing. Every caller
must check PageTail(page), otherwise atomic_inc(&page->_mapcount) is
simply wrong if this page is compound-trans-head.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Jones <davej@redhat.com>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
include/linux/mm.h | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
(limited to 'include')
diff --git a/include/linux/mm.h b/include/linux/mm.h
index f95c71b7c1fd..58202c26c559 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -445,13 +445,12 @@ static inline bool compound_tail_refcounted(struct page *page)
static inline void get_huge_page_tail(struct page *page)
{
/*
- * __split_huge_page_refcount() cannot run
- * from under us.
- * In turn no need of compound_trans_head here.
+ * __split_huge_page_refcount() cannot run from under us.
*/
+ VM_BUG_ON(!PageTail(page));
VM_BUG_ON(page_mapcount(page) < 0);
VM_BUG_ON(atomic_read(&page->_count) != 0);
- if (compound_tail_refcounted(compound_head(page)))
+ if (compound_tail_refcounted(page->first_page))
atomic_inc(&page->_mapcount);
}
--
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