linux-kernel - Re: [PATCH] mm/memblock.c: fix index adjustment error in __next_mem_range

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Date:	Tue, 26 Jul 2016 12:50:40 -0400
From:	Tejun Heo <tj@...nel.org>
To:	zijun_hu@....com
Cc:	akpm@...ux-foundation.org, kuleshovmail@...il.com,
	ard.biesheuvel@...aro.org, tangchen@...fujitsu.com,
	weiyang@...ux.vnet.ibm.com, dev@...l1n.net,
	david@...son.dropbear.id.au, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, zhiyuan_zhu@....com
Subject: Re: [PATCH] mm/memblock.c: fix index adjustment error in
 __next_mem_range_rev()

Hello,

On Tue, Jul 26, 2016 at 03:03:58PM +0000, zijun_hu@....com wrote:
> I am sorry, I don't take any test for the patch attached in previous
> mail, and it can't fix the bug completely, please ignore it I
> provide a new patch attached in this mail which pass test and can
> fix the issue described below
>
> __next_mem_range_rev() defined in mm/memblock.c doesn't Achieve
> desired purpose if parameter type_b ==NULL This new patch can fix
> the issue and get the last reversed region contained in type_a
> rightly

Can you please flow future mails to 80 column?

> The new patch is descripted as follows
> 
> From 0e242eda7696f176a9a2e585a1db01f0575b39c9 Mon Sep 17 00:00:00 2001
> From: zijun_hu <zijun_hu@....com>
> Date: Mon, 25 Jul 2016 15:06:57 +0800
> Subject: [PATCH] mm/memblock.c: fix index adjustment error in
>  __next_mem_range_rev()
> 
> fix region index adjustment error when parameter type_b of
> __next_mem_range_rev() == NULL

The patch is now fixing two bugs.  It'd be nice to describe each in
the description and how the patch was tested.

> @@ -991,7 +991,11 @@ void __init_memblock __next_mem_range_rev(u64 *idx, int nid, ulong flags,
>  
>  	if (*idx == (u64)ULLONG_MAX) {
>  		idx_a = type_a->cnt - 1;
> -		idx_b = type_b->cnt;
> +		/* in order to get the last reversed region rightly */

Before, it would trigger null deref.  I don't think the above comment
is necessary.

> +		if (type_b != NULL)
> +			idx_b = type_b->cnt;
> +		else
> +			idx_b = 0;
>  	}
>  
>  	for (; idx_a >= 0; idx_a--) {
> @@ -1024,7 +1028,7 @@ void __init_memblock __next_mem_range_rev(u64 *idx, int nid, ulong flags,
>  				*out_end = m_end;
>  			if (out_nid)
>  				*out_nid = m_nid;
> -			idx_a++;
> +			idx_a--;
>  			*idx = (u32)idx_a | (u64)idx_b << 32;
>  			return;
>  		}

Both changes look good to me.  Provided the changes are tested,

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun