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Subject[PATCH 3/4] hugetlb, rmap: fix confusing page locking in hugetlb_cow()
Date
if(!trylock_page) block in avoidcopy path of hugetlb_cow() looks confusing
and is buggy. Originally this trylock_page() is intended to make sure
that old_page is locked even when old_page != pagecache_page, because then
only pagecache_page is locked.
This patch fixes it by moving page locking into hugetlb_fault().

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
mm/hugetlb.c | 20 ++++++++++----------
1 files changed, 10 insertions(+), 10 deletions(-)

diff --git v2.6.36-rc3/mm/hugetlb.c v2.6.36-rc3/mm/hugetlb.c
index 9519f3f..2e17e0e 100644
--- v2.6.36-rc3/mm/hugetlb.c
+++ v2.6.36-rc3/mm/hugetlb.c
@@ -2324,11 +2324,8 @@ retry_avoidcopy:
* and just make the page writable */
avoidcopy = (page_mapcount(old_page) == 1);
if (avoidcopy) {
- if (!trylock_page(old_page)) {
- if (PageAnon(old_page))
- page_move_anon_rmap(old_page, vma, address);
- } else
- unlock_page(old_page);
+ if (PageAnon(old_page))
+ page_move_anon_rmap(old_page, vma, address);
set_huge_ptep_writable(vma, address, ptep);
return 0;
}
@@ -2631,10 +2628,14 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
vma, address);
}

- if (!pagecache_page) {
- page = pte_page(entry);
+ /*
+ * hugetlb_cow() requires page locks of pte_page(entry) and
+ * pagecache_page, so here we need take the former one
+ * when page != pagecache_page or !pagecache_page.
+ */
+ page = pte_page(entry);
+ if (page != pagecache_page)
lock_page(page);
- }

spin_lock(&mm->page_table_lock);
/* Check for a racing update before calling hugetlb_cow */
@@ -2661,9 +2662,8 @@ out_page_table_lock:
if (pagecache_page) {
unlock_page(pagecache_page);
put_page(pagecache_page);
- } else {
- unlock_page(page);
}
+ unlock_page(page);

out_mutex:
mutex_unlock(&hugetlb_instantiation_mutex);
--
1.7.2.2


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