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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>
This commit is contained in:
Oleg Nesterov 2014-01-21 15:49:04 -08:00 committed by Linus Torvalds
parent c728852f5d
commit 5eaf1a9e23
1 changed files with 3 additions and 4 deletions
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7
include/linux/mm.h
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@ -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);
}