2021-03-30 12:09:24

by zhouchuangao

Subject: [PATCH] kernel/module: Use BUG_ON instead of if condition followed by BUG.

It can be optimized at compile time.

Signed-off-by: zhouchuangao <[email protected]>
---
kernel/module.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 3047935..f46fc4f 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1014,8 +1014,8 @@ void __symbol_put(const char *symbol)
};

preempt_disable();
- if (!find_symbol(&fsa))
- BUG();
+ BUG_ON(!find_symbol(&fsa));
+
module_put(fsa.owner);
preempt_enable();
}
--
2.7.4

2021-04-13 02:31:48

by Jessica Yu

Subject: Re: [PATCH] kernel/module: Use BUG_ON instead of if condition followed by BUG.

+++ zhouchuangao [30/03/21 05:07 -0700]:
>It can be optimized at compile time.
>
>Signed-off-by: zhouchuangao <[email protected]>

Hi,

Could you please provide a more descriptive changelog? I.e., Is this
a fix for a cocinelle warning? What are the optimization(s)?

Thanks,

Jessica

>---
> kernel/module.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/kernel/module.c b/kernel/module.c
>index 3047935..f46fc4f 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -1014,8 +1014,8 @@ void __symbol_put(const char *symbol)
> };
>
> preempt_disable();
>- if (!find_symbol(&fsa))
>- BUG();
>+ BUG_ON(!find_symbol(&fsa));
>+
> module_put(fsa.owner);
> preempt_enable();
> }
>--
>2.7.4
>

2021-04-13 13:46:13

by zhouchuangao

Subject: Re:Re: [PATCH] kernel/module: Use BUG_ON instead of if condition followed by BUG.

>+++ zhouchuangao [30/03/21 05:07 -0700]:
>>It can be optimized at compile time.
>>
>>Signed-off-by: zhouchuangao <[email protected]>
>
>Hi,
>
>Could you please provide a more descriptive changelog? I.e., Is this
>a fix for a cocinelle warning? What are the optimization(s)?
>
>Thanks,
>
First,
This patch comes from cocinelle warning.

Second,
#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)

BUG_ON uses unlikely in if(). Through disassembly, we can see that
brk #0x800 is compiled to the end of the function.
As you can see below:
......
ffffff8008660bec: d65f03c0 ret
ffffff8008660bf0: d4210000 brk #0x800

Usually, the condition in if () is not satisfied. For the multi-stage pipeline,
we do not need to perform fetch decode and excute operation on brk
instruction.

In my opinion, this can improve the efficiency of the multi-stage pipeline.

Thanks,
zhouchuangao

>Jessica
>
>>---
>> kernel/module.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>>diff --git a/kernel/module.c b/kernel/module.c
>>index 3047935..f46fc4f 100644
>>--- a/kernel/module.c
>>+++ b/kernel/module.c
>>@@ -1014,8 +1014,8 @@ void __symbol_put(const char *symbol)
>> };
>>
>> preempt_disable();
>>- if (!find_symbol(&fsa))
>>- BUG();
>>+ BUG_ON(!find_symbol(&fsa));
>>+
>> module_put(fsa.owner);
>> preempt_enable();
>> }
>>--
>>2.7.4
>>

2021-04-13 15:10:48

by Jessica Yu

Subject: Re: Re: [PATCH] kernel/module: Use BUG_ON instead of if condition followed by BUG.

+++ 周传高 [13/04/21 15:21 +0800]:
>
>>+++ zhouchuangao [30/03/21 05:07 -0700]:
>>>It can be optimized at compile time.
>>>
>>>Signed-off-by: zhouchuangao <[email protected]>
>>
>>Hi,
>>
>>Could you please provide a more descriptive changelog? I.e., Is this
>>a fix for a cocinelle warning? What are the optimization(s)?
>>
>>Thanks,
>>
>First,
>This patch comes from cocinelle warning.
>
>Second,
>#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
>
>BUG_ON uses unlikely in if(). Through disassembly, we can see that
>brk #0x800 is compiled to the end of the function.
>As you can see below:
> ......
> ffffff8008660bec: d65f03c0 ret
> ffffff8008660bf0: d4210000 brk #0x800
>
>Usually, the condition in if () is not satisfied. For the multi-stage pipeline,
>we do not need to perform fetch decode and excute operation on brk
>instruction.
>
>In my opinion, this can improve the efficiency of the multi-stage pipeline.

Thanks. Could you please modify your commit/changelog message to
include this information (including the coccinelle warning) and resend
the patch?