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Subject[PATCH 01/21] mm: hugetlb truncation fixes
hugetlbfs allows truncation of its files (should it?), but hugetlb.c
often forgets that: crashes and misaccounting ensue.

copy_hugetlb_page_range better grab the src page_table_lock since we
don't want to guess what happens if concurrently truncated.
unmap_hugepage_range rss accounting must not assume the full range was
mapped. follow_hugetlb_page must guard with page_table_lock and be
prepared to exit early.

Restyle copy_hugetlb_page_range with a for loop like the others there.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---
mm/hugetlb.c | 35 +++++++++++++++++++++--------------
1 files changed, 21 insertions(+), 14 deletions(-)
--- 2.6.14-rc2/mm/hugetlb.c 2005-09-22 12:32:03.000000000 +0100
+++ mm01/mm/hugetlb.c 2005-09-24 19:26:24.000000000 +0100
@@ -273,21 +273,22 @@ int copy_hugetlb_page_range(struct mm_st
{
pte_t *src_pte, *dst_pte, entry;
struct page *ptepage;
- unsigned long addr = vma->vm_start;
- unsigned long end = vma->vm_end;
+ unsigned long addr;

- while (addr < end) {
+ for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
dst_pte = huge_pte_alloc(dst, addr);
if (!dst_pte)
goto nomem;
+ spin_lock(&src->page_table_lock);
src_pte = huge_pte_offset(src, addr);
- BUG_ON(!src_pte || pte_none(*src_pte)); /* prefaulted */
- entry = *src_pte;
- ptepage = pte_page(entry);
- get_page(ptepage);
- add_mm_counter(dst, rss, HPAGE_SIZE / PAGE_SIZE);
- set_huge_pte_at(dst, addr, dst_pte, entry);
- addr += HPAGE_SIZE;
+ if (src_pte && !pte_none(*src_pte)) {
+ entry = *src_pte;
+ ptepage = pte_page(entry);
+ get_page(ptepage);
+ add_mm_counter(dst, rss, HPAGE_SIZE / PAGE_SIZE);
+ set_huge_pte_at(dst, addr, dst_pte, entry);
+ }
+ spin_unlock(&src->page_table_lock);
}
return 0;

@@ -322,8 +323,8 @@ void unmap_hugepage_range(struct vm_area

page = pte_page(pte);
put_page(page);
+ add_mm_counter(mm, rss, - (HPAGE_SIZE / PAGE_SIZE));
}
- add_mm_counter(mm, rss, -((end - start) >> PAGE_SHIFT));
flush_tlb_range(vma, start, end);
}

@@ -402,6 +403,7 @@ int follow_hugetlb_page(struct mm_struct
BUG_ON(!is_vm_hugetlb_page(vma));

vpfn = vaddr/PAGE_SIZE;
+ spin_lock(&mm->page_table_lock);
while (vaddr < vma->vm_end && remainder) {

if (pages) {
@@ -414,8 +416,13 @@ int follow_hugetlb_page(struct mm_struct
* indexing below to work. */
pte = huge_pte_offset(mm, vaddr & HPAGE_MASK);

- /* hugetlb should be locked, and hence, prefaulted */
- WARN_ON(!pte || pte_none(*pte));
+ /* the hugetlb file might have been truncated */
+ if (!pte || pte_none(*pte)) {
+ remainder = 0;
+ if (!i)
+ i = -EFAULT;
+ break;
+ }

page = &pte_page(*pte)[vpfn % (HPAGE_SIZE/PAGE_SIZE)];

@@ -433,7 +440,7 @@ int follow_hugetlb_page(struct mm_struct
--remainder;
++i;
}
-
+ spin_unlock(&mm->page_table_lock);
*length = remainder;
*position = vaddr;

-
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