2018-10-13 16:16:05

by Peng Hao

Subject: [PATCH] mm/sparse: remove a check that compare if unsigned variable is negative

From: Peng Hao <[email protected]>

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 <[email protected]>
---
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

2018-10-13 17:06:07

by Pavel Tatashin

Subject: Re: [PATCH] mm/sparse: remove a check that compare if unsigned variable is negative

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 <[email protected]> wrote:
>
>
> From: Peng Hao <[email protected]>
>
> 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 <[email protected]>
> ---
> 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
>
>

2018-10-19 08:29:14

by Wei Yang

Subject: Re: [PATCH] mm/sparse: remove a check that compare if unsigned variable is negative

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
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