Commit 07cc2c93 authored by Zhen Lei's avatar Zhen Lei Committed by Alexei Starovoitov
Browse files

livepatch: Improve the search performance of module_kallsyms_on_each_symbol() 



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.

Let's add a new parameter 'const char *modname' to function
module_kallsyms_on_each_symbol(), then we can compare the module names
directly in this function and call hook 'fn' after matching. If 'modname'
is NULL, the symbols of all modules are still traversed for compatibility
with other usage cases.

Phase1: mod1-->mod2..(subsequent modules do not need to be compared)
                |
Phase2:          -->f1-->f2-->f3

Assuming that there are m modules, each module has n symbols on average,
then the time complexity is reduced from O(m * n) to O(m) + O(n).

Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Acked-by: default avatarSong Liu <song@kernel.org>
Signed-off-by: default avatarZhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Acked-by: default avatarMiroslav Benes <mbenes@suse.cz>
Reviewed-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20230116101009.23694-2-jolsa@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 92afc532

include/linux/module.h

+4 −2
Original line number Diff line number Diff line
@@ -879,11 +879,13 @@ static inline bool module_sig_ok(struct module *module) 
#endif	/* CONFIG_MODULE_SIG */



#if defined(CONFIG_MODULES) && defined(CONFIG_KALLSYMS)

int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,

int module_kallsyms_on_each_symbol(const char *modname,

				   int (*fn)(void *, const char *,

					     struct module *, unsigned long),

				   void *data);

#else

static inline int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,

static inline int module_kallsyms_on_each_symbol(const char *modname,

						 int (*fn)(void *, const char *,

						 struct module *, unsigned long),

						 void *data)

{

kernel/livepatch/core.c

+1 −9
Original line number Diff line number Diff line
@@ -118,7 +118,6 @@ 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;
@@ -148,15 +147,9 @@ static int klp_find_callback(void *data, const char *name, 
{

	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;



	return klp_match_callback(data, addr);

}
@@ -164,7 +157,6 @@ 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,
@@ -172,7 +164,7 @@ 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);

kernel/module/kallsyms.c

+12 −1
Original line number Diff line number Diff line
@@ -494,7 +494,8 @@ unsigned long module_kallsyms_lookup_name(const char *name) 
	return ret;

}



int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,

int module_kallsyms_on_each_symbol(const char *modname,

				   int (*fn)(void *, const char *,

					     struct module *, unsigned long),

				   void *data)

{
@@ -509,6 +510,9 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, 
		if (mod->state == MODULE_STATE_UNFORMED)

			continue;



		if (modname && strcmp(modname, mod->name))

			continue;



		/* Use rcu_dereference_sched() to remain compliant with the sparse tool */

		preempt_disable();

		kallsyms = rcu_dereference_sched(mod->kallsyms);
@@ -525,6 +529,13 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, 
			if (ret != 0)

				goto out;

		}



		/*

		 * The given module is found, the subsequent modules do not

		 * need to be compared.

		 */

		if (modname)

			break;

	}

out:

	mutex_unlock(&module_mutex);

kernel/trace/bpf_trace.c

+1 −1
Original line number Diff line number Diff line
@@ -2735,7 +2735,7 @@ static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u3 
	int err;



	/* We return either err < 0 in case of error, ... */

	err = module_kallsyms_on_each_symbol(module_callback, &args);

	err = module_kallsyms_on_each_symbol(NULL, module_callback, &args);

	if (err) {

		kprobe_multi_put_modules(args.mods, args.mods_cnt);

		kfree(args.mods);

kernel/trace/ftrace.c

+1 −1
Original line number Diff line number Diff line
@@ -8324,7 +8324,7 @@ int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *a 
	found_all = kallsyms_on_each_symbol(kallsyms_callback, &args);

	if (found_all)

		return 0;

	found_all = module_kallsyms_on_each_symbol(kallsyms_callback, &args);

	found_all = module_kallsyms_on_each_symbol(NULL, kallsyms_callback, &args);

	return found_all ? 0 : -ESRCH;

}