linux-kernel - Re: [PATCH resend] init/main.c: Simplify initcall

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Date:	Tue, 22 Mar 2016 13:57:28 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Oleg Nesterov <oleg@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH resend] init/main.c: Simplify initcall_blacklisted()

Rasmus Villemoes <linux@...musvillemoes.dk> writes:
> Using kasprintf to get the function name makes us look up the name
> twice, along with all the vsnprintf overhead of parsing the format
> string etc. It also means there is an allocation failure case to deal
> with. Since symbol_string in vsprintf.c would anyway allocate an array
> of size KSYM_SYMBOL_LEN on the stack, that might as well be done up
> here.
>
> Moreover, since this is a debug feature and the blacklisted_initcalls
> list is usually empty, we might as well test that and thus avoid
> looking up the symbol name even once in the common case.
>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>

Acked-by: Rusty Russell <rusty@...tcorp.com.au>

Thanks!
Rusty.

> ---
>  init/main.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/init/main.c b/init/main.c
> index b3c6e363ae18..d76d94cd537c 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -706,21 +706,20 @@ static int __init initcall_blacklist(char *str)
>  static bool __init_or_module initcall_blacklisted(initcall_t fn)
>  {
>  	struct blacklist_entry *entry;
> -	char *fn_name;
> +	char fn_name[KSYM_SYMBOL_LEN];
>  
> -	fn_name = kasprintf(GFP_KERNEL, "%pf", fn);
> -	if (!fn_name)
> +	if (list_empty(&blacklisted_initcalls))
>  		return false;
>  
> +	sprint_symbol_no_offset(fn_name, (unsigned long)fn);
> +
>  	list_for_each_entry(entry, &blacklisted_initcalls, next) {
>  		if (!strcmp(fn_name, entry->buf)) {
>  			pr_debug("initcall %s blacklisted\n", fn_name);
> -			kfree(fn_name);
>  			return true;
>  		}
>  	}
>  
> -	kfree(fn_name);
>  	return false;
>  }
>  #else
> -- 
> 2.1.4