On 08/10/2016 05:28 AM, Andrew Morton wrote:
> On Fri, 5 Aug 2016 23:48:21 +0800 zijun_hu <zijun_hu@xxxxxxxx> wrote:
>
>> From: zijun_hu <zijun_hu@xxxxxxx>
>> Date: Fri, 5 Aug 2016 22:10:07 +0800
>> Subject: [PATCH 1/1] 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
>>
>> get_order_long() is implemented and used instead of fls_long() for
>> fixing the bug
>
> Makes sense. I think.
>
>> --- a/include/linux/bitops.h
>> +++ b/include/linux/bitops.h
>> @@ -192,6 +192,23 @@ static inline unsigned fls_long(unsigned long l)
>> }
>>
>> /**
>> + * get_order_long - get order after rounding @l up to power of 2
>> + * @l: parameter
>> + *
>> + * it is same as get_count_order() but long type parameter
>> + * or 0 is returned if @l == 0UL
>> + */
>> +static inline int get_order_long(unsigned long l)
>> +{
>> + if (l == 0UL)
>> + return 0;
>> + else if (l & (l - 1UL))
>> + return fls_long(l);
>> + else
>> + return fls_long(l) - 1;
>> +}
>> +
>> +/**
>> * __ffs64 - find first set bit in a 64 bit word
>> * @word: The 64 bit word
>> *
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index 91f44e7..7d717f3 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -1360,7 +1360,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
>>
>> BUG_ON(in_interrupt());
>> if (flags & VM_IOREMAP)
>> - align = 1ul << clamp_t(int, fls_long(size),
>> + align = 1ul << clamp_t(int, get_order_long(size),
>> PAGE_SHIFT, IOREMAP_MAX_ORDER);
>>
>> size = PAGE_ALIGN(size);
>
> It would be better to call this get_count_order_long(), I think? To
> match get_count_order()?
>
yes, i agree with you to correct function name
i provide another patch called v2 based on your suggestion as shown below
it have following correction against original patch v1
1) use name get_count_order_long() instead of get_order_long()
2) return -1 if @l == 0 to consist with get_order_long()
3) cast type to int before returning from get_count_order_long()
4) move up function parameter checking for __get_vm_area_node()
5) more commit message is offered to make issue and approach clear
any comments about new patch is welcome
this new patch called patch v2 is shown below
>From 868d3c100f41e16136eed50e47bbfb03d4a16d25 Mon Sep 17 00:00:00 2001
From: zijun_hu <zijun_hu@xxxxxxx>
Date: Wed, 10 Aug 2016 12:13:41 +0800
Subject: [PATCH v2 1/1] 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, for example
size=0x10000 -> fls_long(0x10000)=17 -> align=0x20000
get_count_order_long() is implemented and used instead of fls_long() for
fixing the bug, for example
size=0x10000 -> get_count_order_long(0x10000)=16 -> align=0x10000
Signed-off-by: zijun_hu <zijun_hu@xxxxxxx>
---
include/linux/bitops.h | 16 ++++++++++++++++
mm/vmalloc.c | 8 ++++----
2 files changed, 20 insertions(+), 4 deletions(-)
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 299e76b..93a07d1 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -192,6 +192,22 @@ static inline unsigned fls_long(unsigned long l)
}
/**
+ * get_count_order_long - get order after rounding @l up to power of 2
+ * @l: parameter
+ *
+ * it is same as get_count_order() but with long type parameter
+ */
+static inline int get_count_order_long(unsigned long l)
+{
+ if (l == 0UL)
+ return -1;
+ else if (l & (l - 1UL))
+ return (int)fls_long(l);
+ else
+ return (int)fls_long(l) - 1;
+}
+
+/**
* __ffs64 - find first set bit in a 64 bit word
* @word: The 64 bit word
*
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 91f44e7..80660a0 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1359,14 +1359,14 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
struct vm_struct *area;
BUG_ON(in_interrupt());
- if (flags & VM_IOREMAP)
- align = 1ul << clamp_t(int, fls_long(size),
- PAGE_SHIFT, IOREMAP_MAX_ORDER);
-
size = PAGE_ALIGN(size);
if (unlikely(!size))
return NULL;
+ if (flags & VM_IOREMAP)
+ align = 1ul << clamp_t(int, get_count_order_long(size),
+ PAGE_SHIFT, IOREMAP_MAX_ORDER);
+
area = kzalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node);
if (unlikely(!area))
return NULL;
--
1.9.1
> get_count_order() is a weird name and perhaps both of these should be
> renamed to things which actually make sense. That's a separate issue.
>
okay, perhaps, another patch is applied to correct this weird name issue
in the future due to it is a separate issue now
we use get_count_order_long() to consist with get_order_long() now
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