On 2016/8/5 5:24, Andrew Morton wrote:
>>
>> 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
>>
>> ...
>>
>> --- 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))
>
> I'm having trouble with this, and a more complete description would
> have helped!
>
> As far as I can tell, the current code will decide the following:
>
> size=0x10000: alignment=0x10000
> size=0x0f000: alignment=0x8000
>
no, the current code doesn't achieve the above results as shown below
size=0x10000 -> fls_long(0x10000)=17 -> alignment=0x20000
size=0x0f000 -> fls_long(0x0f000)=16 -> alignment=0x10000
it is wrong for power of 2 value such as size=0x10000
> And your patch will change it so that
>
> size=0x10000: alignment=0x8000
> size=0x0f000: alignment=0x8000
>
> Correct?
>
no, my patch will results in the following calculations
size=0x10000: alignment=0x10000
size=0x0f000: alignment=0x10000
> If so, I'm struggling to see the sense in this. Shouldn't we be
> changing things so that
>
> size=0x10000: alignment=0x10000
> size=0x0f000: alignment=0x10000
>
> ?
okay, it is the aim of my patch as explained above
i provide another solution as shown below
i appreciate it since it is more canonical
please help to review and apply it kindly
>From 1fa79b706735908b2c7aed635dcad7ed9c0a2a87 Mon Sep 17 00:00:00 2001
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
Signed-off-by: zijun_hu <zijun_hu@xxxxxxx>
---
include/linux/bitops.h | 17 +++++++++++++++++
mm/vmalloc.c | 2 +-
2 files changed, 18 insertions(+), 1 deletion(-)
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 299e76b..c18448d 100644
--- 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);
--
1.9.1
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