Re: [PATCH v8 7/9] livepatch: Improve the search performance of module_kallsyms_on_each_symbol()

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Nov 02, 2022 at 04:49:19PM +0800, Zhen Lei wrote:
> Currently we traverse all symbols of all modules to find the specified
> function for the specified module. But in reality, we just need to find
> the given module and then traverse all the symbols in it.

hi,
sorry for delayed answer, I did not notice this until Stephen's email
about merge issue with recent bpf change [1]

> 
> Let's add a new parameter 'const char *modname' to function
> module_kallsyms_on_each_symbol(), then we can compare the module names

we have use case for iterating all modules and their symbols when we
want to resolve passed addresses for tracing

we don't have 'modname' that we could pass, we need to iterate all modules

so perhaps this could be made optional like with passing NULL for modname?

> directly in this function and call hook 'fn' after matching. And the
> parameter 'struct module *' in the hook 'fn' can also be deleted.

we need 'struct module *' argument in the callback as well because we are
taking the module reference if we trace function in it, so it wont get
unloaded

please let me know if I should do the change or can help in any way

thanks,
jirka

[1] https://lore.kernel.org/lkml/20221114111350.38e44eec@canb.auug.org.au/

> 
> Phase1: mod1-->mod2..(subsequent modules do not need to be compared)
>                 |
> Phase2:          -->f1-->f2-->f3
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> ---
>  include/linux/module.h   |  4 ++--
>  kernel/livepatch/core.c  | 13 ++-----------
>  kernel/module/kallsyms.c | 15 ++++++++++++---
>  3 files changed, 16 insertions(+), 16 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index ec61fb53979a92a..0a3b44ff885a48c 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -879,8 +879,8 @@ static inline bool module_sig_ok(struct module *module)
>  }
>  #endif	/* CONFIG_MODULE_SIG */
>  
> -int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
> -					     struct module *, unsigned long),
> +int module_kallsyms_on_each_symbol(const char *modname,
> +				   int (*fn)(void *, const char *, unsigned long),
>  				   void *data);
>  
>  #endif /* _LINUX_MODULE_H */
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 50bfc3481a4ee38..d4fe2d1b0e562bc 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -118,27 +118,19 @@ static struct klp_object *klp_find_object(struct klp_patch *patch,
>  }
>  
>  struct klp_find_arg {
> -	const char *objname;
>  	const char *name;
>  	unsigned long addr;
>  	unsigned long count;
>  	unsigned long pos;
>  };
>  
> -static int klp_find_callback(void *data, const char *name,
> -			     struct module *mod, unsigned long addr)
> +static int klp_find_callback(void *data, const char *name, unsigned long addr)
>  {
>  	struct klp_find_arg *args = data;
>  
> -	if ((mod && !args->objname) || (!mod && args->objname))
> -		return 0;
> -
>  	if (strcmp(args->name, name))
>  		return 0;
>  
> -	if (args->objname && strcmp(args->objname, mod->name))
> -		return 0;
> -
>  	args->addr = addr;
>  	args->count++;
>  
> @@ -175,7 +167,6 @@ static int klp_find_object_symbol(const char *objname, const char *name,
>  				  unsigned long sympos, unsigned long *addr)
>  {
>  	struct klp_find_arg args = {
> -		.objname = objname,
>  		.name = name,
>  		.addr = 0,
>  		.count = 0,
> @@ -183,7 +174,7 @@ static int klp_find_object_symbol(const char *objname, const char *name,
>  	};
>  
>  	if (objname)
> -		module_kallsyms_on_each_symbol(klp_find_callback, &args);
> +		module_kallsyms_on_each_symbol(objname, klp_find_callback, &args);
>  	else
>  		kallsyms_on_each_match_symbol(klp_match_callback, name, &args);
>  
> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
> index f5c5c9175333df7..329cef573675d49 100644
> --- a/kernel/module/kallsyms.c
> +++ b/kernel/module/kallsyms.c
> @@ -495,8 +495,8 @@ unsigned long module_kallsyms_lookup_name(const char *name)
>  }
>  
>  #ifdef CONFIG_LIVEPATCH
> -int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
> -					     struct module *, unsigned long),
> +int module_kallsyms_on_each_symbol(const char *modname,
> +				   int (*fn)(void *, const char *, unsigned long),
>  				   void *data)
>  {
>  	struct module *mod;
> @@ -510,6 +510,9 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
>  		if (mod->state == MODULE_STATE_UNFORMED)
>  			continue;
>  
> +		if (strcmp(modname, mod->name))
> +			continue;
> +
>  		/* Use rcu_dereference_sched() to remain compliant with the sparse tool */
>  		preempt_disable();
>  		kallsyms = rcu_dereference_sched(mod->kallsyms);
> @@ -522,10 +525,16 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
>  				continue;
>  
>  			ret = fn(data, kallsyms_symbol_name(kallsyms, i),
> -				 mod, kallsyms_symbol_value(sym));
> +				 kallsyms_symbol_value(sym));
>  			if (ret != 0)
>  				goto out;
>  		}
> +
> +		/*
> +		 * The given module is found, the subsequent modules do not
> +		 * need to be compared.
> +		 */
> +		break;
>  	}
>  out:
>  	mutex_unlock(&module_mutex);
> -- 
> 2.25.1
>