mm: thp: fix /dev/zero MAP_PRIVATE and vm_flags cleanups

The huge_memory.c THP page fault was allowed to run if vm_ops was null
(which would succeed for /dev/zero MAP_PRIVATE, as the f_op->mmap wouldn't
setup a special vma->vm_ops and it would fallback to regular anonymous
memory) but other THP logics weren't fully activated for vmas with vm_file
not NULL (/dev/zero has a not NULL vma->vm_file).

So this removes the vm_file checks so that /dev/zero also can safely use
THP (the other albeit safer approach to fix this bug would have been to
prevent the THP initial page fault to run if vm_file was set).

After removing the vm_file checks, this also makes huge_memory.c stricter
in khugepaged for the DEBUG_VM=y case.  It doesn't replace the vm_file
check with a is_pfn_mapping check (but it keeps checking for VM_PFNMAP
under VM_BUG_ON) because for a is_cow_mapping() mapping VM_PFNMAP should
only be allowed to exist before the first page fault, and in turn when
vma->anon_vma is null (so preventing khugepaged registration).  So I tend
to think the previous comment saying if vm_file was set, VM_PFNMAP might
have been set and we could still be registered in khugepaged (despite
anon_vma was not NULL to be registered in khugepaged) was too paranoid.
The is_linear_pfn_mapping check is also I think superfluous (as described
by comment) but under DEBUG_VM it is safe to stay.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=33682

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Caspar Zhang <bugs@casparzhang.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: <stable@kernel.org>		[2.6.38.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index df29c8f..8847c8c 100644 (file)
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -117,7 +117,7 @@ static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
                                         unsigned long end,
                                         long adjust_next)
 {
-       if (!vma->anon_vma || vma->vm_ops || vma->vm_file)
+       if (!vma->anon_vma || vma->vm_ops)
                return;
        __vma_adjust_trans_huge(vma, start, end, adjust_next);
 }

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 692dbae..2348db2 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -137,7 +137,8 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_RandomReadHint(v)           ((v)->vm_flags & VM_RAND_READ)
 
 /*
- * special vmas that are non-mergable, non-mlock()able
+ * Special vmas that are non-mergable, non-mlock()able.
+ * Note: mm/huge_memory.c VM_NO_THP depends on this definition.
  */
 #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP)
 

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 470dcda..83326ad 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1408,6 +1408,9 @@ out:
        return ret;
 }
 
+#define VM_NO_THP (VM_SPECIAL|VM_INSERTPAGE|VM_MIXEDMAP|VM_SAO| \
+                  VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
+
 int hugepage_madvise(struct vm_area_struct *vma,
                     unsigned long *vm_flags, int advice)
 {
@@ -1416,11 +1419,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
                /*
                 * Be somewhat over-protective like KSM for now!
                 */
-               if (*vm_flags & (VM_HUGEPAGE |
-                                VM_SHARED   | VM_MAYSHARE   |
-                                VM_PFNMAP   | VM_IO      | VM_DONTEXPAND |
-                                VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
-                                VM_MIXEDMAP | VM_SAO))
+               if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
                        return -EINVAL;
                *vm_flags &= ~VM_NOHUGEPAGE;
                *vm_flags |= VM_HUGEPAGE;
@@ -1436,11 +1435,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
                /*
                 * Be somewhat over-protective like KSM for now!
                 */
-               if (*vm_flags & (VM_NOHUGEPAGE |
-                                VM_SHARED   | VM_MAYSHARE   |
-                                VM_PFNMAP   | VM_IO      | VM_DONTEXPAND |
-                                VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
-                                VM_MIXEDMAP | VM_SAO))
+               if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
                        return -EINVAL;
                *vm_flags &= ~VM_HUGEPAGE;
                *vm_flags |= VM_NOHUGEPAGE;
@@ -1574,10 +1569,14 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
                 * page fault if needed.
                 */
                return 0;
-       if (vma->vm_file || vma->vm_ops)
+       if (vma->vm_ops)
                /* khugepaged not yet working on file or special mappings */
                return 0;
-       VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma));
+       /*
+        * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
+        * true too, verify it here.
+        */
+       VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags & VM_NO_THP);
        hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
        hend = vma->vm_end & HPAGE_PMD_MASK;
        if (hstart < hend)
@@ -1828,12 +1827,15 @@ static void collapse_huge_page(struct mm_struct *mm,
            (vma->vm_flags & VM_NOHUGEPAGE))
                goto out;
 
-       /* VM_PFNMAP vmas may have vm_ops null but vm_file set */
-       if (!vma->anon_vma || vma->vm_ops || vma->vm_file)
+       if (!vma->anon_vma || vma->vm_ops)
                goto out;
        if (is_vma_temporary_stack(vma))
                goto out;
-       VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma));
+       /*
+        * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
+        * true too, verify it here.
+        */
+       VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags & VM_NO_THP);
 
        pgd = pgd_offset(mm, address);
        if (!pgd_present(*pgd))
@@ -2066,13 +2068,16 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
                        progress++;
                        continue;
                }
-               /* VM_PFNMAP vmas may have vm_ops null but vm_file set */
-               if (!vma->anon_vma || vma->vm_ops || vma->vm_file)
+               if (!vma->anon_vma || vma->vm_ops)
                        goto skip;
                if (is_vma_temporary_stack(vma))
                        goto skip;
-
-               VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma));
+               /*
+                * If is_pfn_mapping() is true is_learn_pfn_mapping()
+                * must be true too, verify it here.
+                */
+               VM_BUG_ON(is_linear_pfn_mapping(vma) ||
+                         vma->vm_flags & VM_NO_THP);
 
                hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
                hend = vma->vm_end & HPAGE_PMD_MASK;