[PATCH] 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>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 21 insertions, 14 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 901ac523a1c3..a1b30d45459e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -274,21 +274,22 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 {
         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;
 
@@ -323,8 +324,8 @@ void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
 
                 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);
 }
 
@@ -403,6 +404,7 @@ int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
         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) {
@@ -415,8 +417,13 @@ int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                          * 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)];
 
@@ -434,7 +441,7 @@ int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 --remainder;
                 ++i;
         }
-
+        spin_unlock(&mm->page_table_lock);
         *length = remainder;
         *position = vaddr;