linux-kernel - Re: [PATCH v8 6/9] livepatch: Use kallsyms_on_each_match

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Date:   Wed, 23 Nov 2022 14:28:24 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-modules@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        David Laight <David.Laight@...lab.com>
Subject: Re: [PATCH v8 6/9] livepatch: Use kallsyms_on_each_match_symbol() to
 improve performance

Hi,

I am sorry for the late review. I have been snowed under another
tasks.

On Wed 2022-11-02 16:49:18, Zhen Lei wrote:
> Based on the test results of kallsyms_on_each_match_symbol() and
> kallsyms_on_each_symbol(), the average performance can be improved by
> more than 1500 times.

Sounds great.

> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -153,6 +153,24 @@ static int klp_find_callback(void *data, const char *name,
>  	return 0;
>  }
>  
> +static int klp_match_callback(void *data, unsigned long addr)
> +{
> +	struct klp_find_arg *args = data;
> +
> +	args->addr = addr;
> +	args->count++;
> +
> +	/*
> +	 * Finish the search when the symbol is found for the desired position
> +	 * or the position is not defined for a non-unique symbol.
> +	 */
> +	if ((args->pos && (args->count == args->pos)) ||
> +	    (!args->pos && (args->count > 1)))
> +		return 1;
> +
> +	return 0;

This duplicates most of the klp_find_callback(). Please, call this
new function in klp_find_callback() instead of the duplicated code.
I mean to do:

static int klp_find_callback(void *data, const char *name, unsigned long addr)
{
	struct klp_find_arg *args = data;

	if (strcmp(args->name, name))
		return 0;

	return klp_match_callback(data, addr);
}

Otherwise, it looks good.

Best Regards,
Petr