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Date: Tue, 06 Mar 2012 19:30:25 -0500
From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
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To: Mikulas Patocka <mpatocka@redhat.com>
CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Hugh Dickins <hughd@google.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Shaohua Li <shaohua.li@intel.com>, Michal Hocko <mhocko@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, kosaki.motohiro@gmail.com
Subject: Re: [PATCH] fix bug introduced in "mm: simplify find_vma_prev()"
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(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@redhat.com>

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


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