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

[Jessica Yu]

+++ zhouchuangao [09/05/21 18:38 -0700]:
> This patch comes from cocinelle warning.

Please include the output of the cocinelle warning here as well.

See commit 56149c8cd820 ("media: pci: saa7164-core.c: replace if
(cond) BUG() with BUG_ON()") for an example. Thanks.

> 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.
>
> Signed-off-by: zhouchuangao <zhouchuangao@xxxxxxxx>
> ---
> kernel/module.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index b5dd92e..faf9114 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1014,8 +1014,7 @@ 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