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mm: vma_merge: correct false positive from __vma_unlink->validate_mm_rb 

The old code was always doing:

   vma->vm_end = next->vm_end
   vma_rb_erase(next) // in __vma_unlink
   vma->vm_next = next->vm_next // in __vma_unlink
   next = vma->vm_next
   vma_gap_update(next)

The new code still does the above for remove_next == 1 and 2, but for
remove_next == 3 it has been changed and it does:

   next->vm_start = vma->vm_start
   vma_rb_erase(vma) // in __vma_unlink
   vma_gap_update(next)

In the latter case, while unlinking "vma", validate_mm_rb() is told to
ignore "vma" that is being removed, but next->vm_start was reduced
instead. So for the new case, to avoid the false positive from
validate_mm_rb, it should be "next" that is ignored when "vma" is
being unlinked.

"vma" and "next" in the above comment, considered pre-swap().

Link: http://lkml.kernel.org/r/1474492522-2261-4-git-send-email-aarcange@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Tested-by: Shaun Tancheff <shaun.tancheff@seagate.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jan Vorlicek <janvorli@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2016-10-07 17:01:37 -07:00 committed by Linus Torvalds
parent 86d12e471d
commit 8f26e0b176
1 changed files with 41 additions and 18 deletions
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59
mm/mmap.c
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@ -402,7 +402,32 @@ static inline void vma_rb_insert(struct vm_area_struct *vma,
rb_insert_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
}
static void vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
static void __vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
{
/*
* Note rb_erase_augmented is a fairly large inline function,
* so make sure we instantiate it only once with our desired
* augmented rbtree callbacks.
*/
rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
}
static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma,
struct rb_root *root,
struct vm_area_struct *ignore)
{
/*
* All rb_subtree_gap values must be consistent prior to erase,
* with the possible exception of the "next" vma being erased if
* next->vm_start was reduced.
*/
validate_mm_rb(root, ignore);
__vma_rb_erase(vma, root);
}
static __always_inline void vma_rb_erase(struct vm_area_struct *vma,
struct rb_root *root)
{
/*
* All rb_subtree_gap values must be consistent prior to erase,
@ -410,12 +435,7 @@ static void vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root)
*/
validate_mm_rb(root, vma);
/*
* Note rb_erase_augmented is a fairly large inline function,
* so make sure we instantiate it only once with our desired
* augmented rbtree callbacks.
*/
rb_erase_augmented(&vma->vm_rb, root, &vma_gap_callbacks);
__vma_rb_erase(vma, root);
}
/*
@ -604,11 +624,12 @@ static void __insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
static __always_inline void __vma_unlink_common(struct mm_struct *mm,
struct vm_area_struct *vma,
struct vm_area_struct *prev,
bool has_prev)
bool has_prev,
struct vm_area_struct *ignore)
{
struct vm_area_struct *next;
vma_rb_erase(vma, &mm->mm_rb);
vma_rb_erase_ignore(vma, &mm->mm_rb, ignore);
next = vma->vm_next;
if (has_prev)
prev->vm_next = next;
@ -630,13 +651,7 @@ static inline void __vma_unlink_prev(struct mm_struct *mm,
struct vm_area_struct *vma,
struct vm_area_struct *prev)
{
__vma_unlink_common(mm, vma, prev, true);
}
static inline void __vma_unlink(struct mm_struct *mm,
struct vm_area_struct *vma)
{
__vma_unlink_common(mm, vma, NULL, false);
__vma_unlink_common(mm, vma, prev, true, vma);
}
/*
@ -815,8 +830,16 @@ again:
if (remove_next != 3)
__vma_unlink_prev(mm, next, vma);
else
/* vma is not before next if they've been swapped */
__vma_unlink(mm, next);
/*
* vma is not before next if they've been
* swapped.
*
* pre-swap() next->vm_start was reduced so
* tell validate_mm_rb to ignore pre-swap()
* "next" (which is stored in post-swap()
* "vma").
*/
__vma_unlink_common(mm, next, NULL, false, vma);
if (file)
__remove_shared_vm_struct(next, file, mapping);
} else if (insert) {