* [PATCH] mm/sparse: remove a check that compare if unsigned variable is negative
@ 2018-10-13 16:15 Peng Hao
2018-10-13 17:04 ` Pavel Tatashin
0 siblings, 1 reply; 4+ messages in thread
From: Peng Hao @ 2018-10-13 16:15 UTC (permalink / raw)
To: linux-mm; +Cc: akpm, pasha.tatashin, osalvador, linux-kernel, Peng Hao
From: Peng Hao <peng.hao2@zte.com.cn>
In all use locations for for_each_present_section_nr, variable
section_nr is unsigned. It is unnecessary to test if it is negative.
Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
---
mm/sparse.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/mm/sparse.c b/mm/sparse.c
index 10b07ee..a6f9f22 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -196,8 +196,7 @@ static inline int next_present_section_nr(int section_nr)
}
#define for_each_present_section_nr(start, section_nr) \
for (section_nr = next_present_section_nr(start-1); \
- ((section_nr >= 0) && \
- (section_nr <= __highest_present_section_nr)); \
+ section_nr <= __highest_present_section_nr; \
section_nr = next_present_section_nr(section_nr))
static inline unsigned long first_present_section_nr(void)
--
1.8.3.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] mm/sparse: remove a check that compare if unsigned variable is negative
2018-10-13 16:15 [PATCH] mm/sparse: remove a check that compare if unsigned variable is negative Peng Hao
@ 2018-10-13 17:04 ` Pavel Tatashin
2018-10-15 1:08 ` [PATCH] mm/sparse: remove a check that compare if unsignedvariable " peng.hao2
2018-10-19 8:28 ` [PATCH] mm/sparse: remove a check that compare if unsigned variable " Wei Yang
0 siblings, 2 replies; 4+ messages in thread
From: Pavel Tatashin @ 2018-10-13 17:04 UTC (permalink / raw)
To: penghao122
Cc: Linux Memory Management List, Andrew Morton, pasha.tatashin,
osalvador, LKML, peng.hao2
This is incorrect: next_present_section_nr() returns "int" and -1 no
next section, this change would lead to infinite loop.
On Sat, Oct 13, 2018 at 12:16 PM Peng Hao <penghao122@sina.com.cn> wrote:
>
>
> From: Peng Hao <peng.hao2@zte.com.cn>
>
> In all use locations for for_each_present_section_nr, variable
> section_nr is unsigned. It is unnecessary to test if it is negative.
>
> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
> ---
> mm/sparse.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 10b07ee..a6f9f22 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -196,8 +196,7 @@ static inline int next_present_section_nr(int section_nr)
> }
> #define for_each_present_section_nr(start, section_nr) \
> for (section_nr = next_present_section_nr(start-1); \
> - ((section_nr >= 0) && \
> - (section_nr <= __highest_present_section_nr)); \
> + section_nr <= __highest_present_section_nr; \
> section_nr = next_present_section_nr(section_nr))
>
> static inline unsigned long first_present_section_nr(void)
> --
> 1.8.3.1
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm/sparse: remove a check that compare if unsignedvariable is negative
2018-10-13 17:04 ` Pavel Tatashin
@ 2018-10-15 1:08 ` peng.hao2
2018-10-19 8:28 ` [PATCH] mm/sparse: remove a check that compare if unsigned variable " Wei Yang
1 sibling, 0 replies; 4+ messages in thread
From: peng.hao2 @ 2018-10-15 1:08 UTC (permalink / raw)
To: pasha.tatashin
Cc: penghao122, linux-mm, akpm, pasha.tatashin, osalvador,
linux-kernel
[-- Attachment #1.1: Type: text/plain, Size: 1321 bytes --]
>This is incorrect: next_present_section_nr() returns "int" and -1 no
>next section, this change would lead to infinite loop.
int x = -1;
unsigned long y = x;
y is never less than 0 . But y is a large positive number.
>On Sat, Oct 13, 2018 at 12:16 PM Peng Hao <penghao122@sina.com.cn> wrote:
>>
>> From: Peng Hao <peng.hao2@zte.com.cn>
>>
>> In all use locations for for_each_present_section_nr, variable
>> section_nr is unsigned. It is unnecessary to test if it is negative.
>>
>> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
>> ---
>> mm/sparse.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/mm/sparse.c b/mm/sparse.c
>> index 10b07ee..a6f9f22 100644
>> --- a/mm/sparse.c
>> +++ b/mm/sparse.c
>> @@ -196,8 +196,7 @@ static inline int next_present_section_nr(int section_nr)
>> }
>> #define for_each_present_section_nr(start, section_nr) \
>> for (section_nr = next_present_section_nr(start-1); \
>> - ((section_nr >= 0) && \
>> - (section_nr <= __highest_present_section_nr)); \
>> + section_nr <= __highest_present_section_nr; \
>> section_nr = next_present_section_nr(section_nr))
>>
>> static inline unsigned long first_present_section_nr(void)
>> --
>> 1.8.3.1
>>
>>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm/sparse: remove a check that compare if unsigned variable is negative
2018-10-13 17:04 ` Pavel Tatashin
2018-10-15 1:08 ` [PATCH] mm/sparse: remove a check that compare if unsignedvariable " peng.hao2
@ 2018-10-19 8:28 ` Wei Yang
1 sibling, 0 replies; 4+ messages in thread
From: Wei Yang @ 2018-10-19 8:28 UTC (permalink / raw)
To: Pavel Tatashin
Cc: penghao122, Linux Memory Management List, Andrew Morton,
pasha.tatashin, osalvador, LKML, peng.hao2
On Sat, Oct 13, 2018 at 01:04:45PM -0400, Pavel Tatashin wrote:
>This is incorrect: next_present_section_nr() returns "int" and -1 no
>next section, this change would lead to infinite loop.
Yes, the -1 is a very special value.
--
Wei Yang
Help you, Help me
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2018-10-19 8:28 UTC | newest]
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2018-10-13 16:15 [PATCH] mm/sparse: remove a check that compare if unsigned variable is negative Peng Hao
2018-10-13 17:04 ` Pavel Tatashin
2018-10-15 1:08 ` [PATCH] mm/sparse: remove a check that compare if unsignedvariable " peng.hao2
2018-10-19 8:28 ` [PATCH] mm/sparse: remove a check that compare if unsigned variable " Wei Yang
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