linux-kernel - Re: [PATCH] fix bug introduced in "mm: simplify find_vma

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Message-ID: <4F56AC21.1050000@gmail.com>
Date:	Tue, 06 Mar 2012 19:30:25 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Mikulas Patocka <mpatocka@...hat.com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Shaohua Li <shaohua.li@...el.com>,
	Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, kosaki.motohiro@...il.com
Subject: Re: [PATCH] fix bug introduced in "mm: simplify find_vma_prev()"

(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@...hat.com>

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


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