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hugetlb: acquire the i_mmap_lock before walking the prio_tree to unmap a page 

When the owner of a mapping fails COW because a child process is holding a
reference, the children VMAs are walked and the page is unmapped.  The
i_mmap_lock is taken for the unmapping of the page but not the walking of
the prio_tree.  In theory, that tree could be changing if the lock is not
held.  This patch takes the i_mmap_lock properly for the duration of the
prio_tree walk.

[hugh.dickins@tiscali.co.uk: Spotted the problem in the first place]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mel Gorman 2009-12-14 17:59:53 -08:00 committed by Linus Torvalds
parent 70da2340fb
commit 4eb2b1dcd5
1 changed files with 8 additions and 1 deletions
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9
mm/hugetlb.c
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@ -2237,6 +2237,12 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
+ (vma->vm_pgoff >> PAGE_SHIFT);
mapping = (struct address_space *)page_private(page);
/*
* Take the mapping lock for the duration of the table walk. As
* this mapping should be shared between all the VMAs,
* __unmap_hugepage_range() is called as the lock is already held
*/
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(iter_vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
/* Do not unmap the current VMA */
if (iter_vma == vma)
@ -2250,10 +2256,11 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
* from the time of fork. This would look like data corruption
*/
if (!is_vma_resv_set(iter_vma, HPAGE_RESV_OWNER))
unmap_hugepage_range(iter_vma,
__unmap_hugepage_range(iter_vma,
address, address + huge_page_size(h),
page);
}
spin_unlock(&mapping->i_mmap_lock);
return 1;
}