Re: [PATCH] fix bug introduced in "mm: simplify find_vma_prev()"

From: KOSAKI Motohiro
Date: Tue Mar 06 2012 - 19:30:16 EST


(3/4/12 7:52 PM), Mikulas Patocka wrote:
Hi

This patch fixes a bug introduced in "mm: simplify find_vma_prev()". You
can apply this, or alternatively revert the original patch.

Mikulas

---

mm: fix find_vma_prev

The commit mm: simplify find_vma_prev()
[6bd4837de96e7d9f9bf33e59117c24fc230862ac] 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@xxxxxxxxxx>

Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>


I prefer to remove find_vma_prev() eventually. but this is good short term solution.
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