Commit 8f26e0b1 authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
Browse files

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: default avatarAndrea Arcangeli <aarcange@redhat.com>
Tested-by: default avatarShaun 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 86d12e47

mm/mmap.c

+41 −18
Original line number Diff line number Diff line
@@ -402,14 +402,8 @@ 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)

{

	/*

	 * All rb_subtree_gap values must be consistent prior to erase,

	 * with the possible exception of the vma being erased.

	 */

	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
@@ -418,6 +412,32 @@ static void vma_rb_erase(struct vm_area_struct *vma, struct rb_root *root) 
	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,

	 * with the possible exception of the vma being erased.

	 */

	validate_mm_rb(root, vma);



	__vma_rb_erase(vma, root);

}



/*

 * vma has some anon_vma assigned, and is already inserted on that

 * anon_vma's interval trees.
@@ -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) {

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