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| author | Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> | 2010-09-10 13:23:04 +0900 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-09-23 17:29:18 -0700 |
| commit | 56c9cfb13c9b6516017eea4e8cbe22ea02e07ee6 (patch) | |
| tree | 1b09c9350d8f48d81514f274a3a1933dc9f1a2ef /mm | |
| parent | cd67f0d2a9a6b5b9f79f4343dc8805757d9ebae2 (diff) | |
| download | lwn-56c9cfb13c9b6516017eea4e8cbe22ea02e07ee6.tar.gz lwn-56c9cfb13c9b6516017eea4e8cbe22ea02e07ee6.zip | |
hugetlb, rmap: fix confusing page locking in hugetlb_cow()
The "if (!trylock_page)" block in the avoidcopy path of hugetlb_cow()
looks confusing and is buggy. Originally this trylock_page() was
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>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/hugetlb.c | 22 |
1 files changed, 12 insertions, 10 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 9519f3f6c1da..c03273807182 100644 --- a/mm/hugetlb.c +++ b/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 +2628,16 @@ 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. + * Note that locking order is always pagecache_page -> page, + * so no worry about deadlock. + */ + 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 +2664,8 @@ 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); |