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mm: fix find_vma_prev

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Commit 6bd4837de9 ("mm: simplify find_vma_prev()") broke memory
management on PA-RISC.

After application of the patch, programs that allocate big arrays on the
stack crash with segfault, for example, this will crash if compiled
without optimization:

  int main()
  {
	char array[200000];
	array[199999] = 0;
	return 0;
  }

The reason is that PA-RISC has up-growing stack and the stack is usually
the last memory area.  In the above example, a page fault happens above
the stack.

Previously, if we passed too high address to find_vma_prev, it returned
NULL and stored the last VMA in *pprev.  After "simplify find_vma_prev"
change, it stores NULL in *pprev.  Consequently, the stack area is not
found and it is not expanded, as it used to be before the change.

This patch restores the old behavior and makes it return the last VMA in
*pprev if the requested address is higher than address of any other VMA.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mikulas Patocka 2012-03-04 19:52:03 -05:00 committed by Linus Torvalds
parent 52abb700e1
commit 83cd904d27
1 changed files with 10 additions and 2 deletions
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12
mm/mmap.c
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@ -1608,7 +1608,6 @@ EXPORT_SYMBOL(find_vma);
/*
* Same as find_vma, but also return a pointer to the previous VMA in *pprev.
* Note: pprev is set to NULL when return value is NULL.
*/
struct vm_area_struct *
find_vma_prev(struct mm_struct *mm, unsigned long addr,
@ -1617,7 +1616,16 @@ find_vma_prev(struct mm_struct *mm, unsigned long addr,
struct vm_area_struct *vma;
vma = find_vma(mm, addr);
*pprev = vma ? vma->vm_prev : NULL;
if (vma) {
*pprev = vma->vm_prev;
} else {
struct rb_node *rb_node = mm->mm_rb.rb_node;
*pprev = NULL;
while (rb_node) {
*pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb);
rb_node = rb_node->rb_right;
}
}
return vma;
}