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Commit 56c9cfb1 authored by Naoya Horiguchi's avatar Naoya Horiguchi Committed by Linus Torvalds
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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: default avatarNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cd67f0d2

mm/hugetlb.c

+12 −10
Original line number Original line Diff line number Diff line
@@ -2324,11 +2324,8 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma, 
	 * and just make the page writable */

	 * and just make the page writable */

	avoidcopy = (page_mapcount(old_page) == 1);

	avoidcopy = (page_mapcount(old_page) == 1);

	if (avoidcopy) {

	if (avoidcopy) {

		if (!trylock_page(old_page)) {

		if (PageAnon(old_page))

		if (PageAnon(old_page))

			page_move_anon_rmap(old_page, vma, address);

			page_move_anon_rmap(old_page, vma, address);

		} else

			unlock_page(old_page);

		set_huge_ptep_writable(vma, address, ptep);

		set_huge_ptep_writable(vma, address, ptep);

		return 0;

		return 0;

	}

	}
@@ -2631,10 +2628,16 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, 
								vma, address);

								vma, address);

	}

	}





	if (!pagecache_page) {

	/*

	 * 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);

	page = pte_page(entry);

	if (page != pagecache_page)

		lock_page(page);

		lock_page(page);

	}





	spin_lock(&mm->page_table_lock);

	spin_lock(&mm->page_table_lock);

	/* Check for a racing update before calling hugetlb_cow */

	/* Check for a racing update before calling hugetlb_cow */
@@ -2661,9 +2664,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, 
	if (pagecache_page) {

	if (pagecache_page) {

		unlock_page(pagecache_page);

		unlock_page(pagecache_page);

		put_page(pagecache_page);

		put_page(pagecache_page);

	} else {

		unlock_page(page);

	}

	}

	unlock_page(page);





out_mutex:

out_mutex:

	mutex_unlock(&hugetlb_instantiation_mutex);

	mutex_unlock(&hugetlb_instantiation_mutex);