linux-kernel - Re: [PATCH] mm/vmalloc: fix align value calculation error

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Date:	Thu, 4 Aug 2016 16:36:11 +0800
From:	zijun_hu <zijun_hu@...o.com>
To:	Andrew Morton <akpm@...ux-foundation.org>, tj@...nel.org,
	hannes@...xchg.org
Cc:	mhocko@...nel.org, minchan@...nel.org, zijun_hu@....com,
	rientjes@...gle.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] mm/vmalloc: fix align value calculation error

On 08/04/2016 04:02 PM, zijun_hu wrote:
>>>From e40d1066f61394992e0167f259001ae9d2581dc1 Mon Sep 17 00:00:00 2001
> From: zijun_hu <zijun_hu@....com>
> Date: Thu, 4 Aug 2016 14:22:52 +0800
> Subject: [PATCH] mm/vmalloc: fix align value calculation error
> 
> it causes double align requirement for __get_vm_area_node() if parameter
> size is power of 2 and VM_IOREMAP is set in parameter flags
> 
> it is fixed by using order_base_2 instead of fls_long() due to lack of
> get_count_order() for long parameter
> 
> Signed-off-by: zijun_hu <zijun_hu@....com>
> ---
>  mm/vmalloc.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 91f44e7..8b17c51 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1357,11 +1357,19 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
>  {
>  	struct vmap_area *va;
>  	struct vm_struct *area;
> +	int ioremap_size_order;
>  
>  	BUG_ON(in_interrupt());
> -	if (flags & VM_IOREMAP)
> -		align = 1ul << clamp_t(int, fls_long(size),
> -				       PAGE_SHIFT, IOREMAP_MAX_ORDER);
> +	if (flags & VM_IOREMAP) {
> +		if (unlikely(size < 2))
> +			ioremap_size_order = size;
> +		else if (unlikely((signed long)size < 0))
> +			ioremap_size_order = sizeof(size) * 8;
> +		else
> +			ioremap_size_order = order_base_2(size);
> +		align = 1ul << clamp_t(int, ioremap_size_order, PAGE_SHIFT,
> +				IOREMAP_MAX_ORDER);
> +	}
>  
>  	size = PAGE_ALIGN(size);
>  	if (unlikely(!size))
> 
another fix approach is shown as follows

From: zijun_hu <zijun_hu@....com>
Date: Thu, 4 Aug 2016 14:22:52 +0800
Subject: [PATCH] mm/vmalloc: fix align value calculation error

it causes double align requirement for __get_vm_area_node() if parameter
size is power of 2 and VM_IOREMAP is set in parameter flags

it is fixed by handling the specail case manually due to lack of
get_count_order() for long parameter

Signed-off-by: zijun_hu <zijun_hu@....com>
---
 mm/vmalloc.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 91f44e7..dbbca8a 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1357,11 +1357,16 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
 {
 	struct vmap_area *va;
 	struct vm_struct *area;
+	int ioremap_size_order;
 
 	BUG_ON(in_interrupt());
-	if (flags & VM_IOREMAP)
-		align = 1ul << clamp_t(int, fls_long(size),
-				       PAGE_SHIFT, IOREMAP_MAX_ORDER);
+	if (flags & VM_IOREMAP) {
+		ioremap_size_order = fls_long(size);
+		if (is_power_of_2(size) && size != 1)
+			ioremap_size_order--;
+		align = 1ul << clamp_t(int, ioremap_size_order, PAGE_SHIFT,
+				IOREMAP_MAX_ORDER);
+	}
 
 	size = PAGE_ALIGN(size);
 	if (unlikely(!size))
-- 
1.9.1