Merge branch 'kallsyms: Optimize the search for module symbols by livepatch and bpf'

Jiri Olsa says:

====================

hi,
sending new version of [1] patchset posted originally by Zhen Lei.
It contains 2 changes that improove search performance for livepatch
and bpf.

v3 changes:
  - fixed off by 1 issue, simplified condition, added acks [Song]
  - added module attach as subtest [Andrii]

v2 changes:
  - reworked the bpf change and meassured the performance
  - adding new selftest to benchmark kprobe multi module attachment
  - skipping patch 3 as requested by Zhen Lei
  - added Reviewed-by for patch 1 [Petr Mladek]

thanks,
jirka

[1] https://lore.kernel.org/bpf/20221230112729.351-1-thunder.leizhen@huawei.com/
---
Jiri Olsa (2):
      selftests/bpf: Add serial_test_kprobe_multi_bench_attach_kernel/module tests
      bpf: Change modules resolving for kprobe multi link
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/module.h

@@ -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

@@ -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

@@ -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

@@ -2682,69 +2682,77 @@ static void symbols_swap_r(void *a, void *b, int size, const void *priv)
 	}
 }
 
-struct module_addr_args {
-	unsigned long *addrs;
-	u32 addrs_cnt;
+struct modules_array {
 	struct module **mods;
 	int mods_cnt;
 	int mods_cap;
 };
 
-static int module_callback(void *data, const char *name,
-			   struct module *mod, unsigned long addr)
+static int add_module(struct modules_array *arr, struct module *mod)
 {
-	struct module_addr_args *args = data;
 	struct module **mods;
 
-	/* We iterate all modules symbols and for each we:
-	 * - search for it in provided addresses array
-	 * - if found we check if we already have the module pointer stored
-	 *   (we iterate modules sequentially, so we can check just the last
-	 *   module pointer)
-	 * - take module reference and store it
-	 */
-	if (!bsearch(&addr, args->addrs, args->addrs_cnt, sizeof(addr),
-		       bpf_kprobe_multi_addrs_cmp))
-		return 0;
-
-	if (args->mods && args->mods[args->mods_cnt - 1] == mod)
-		return 0;
-
-	if (args->mods_cnt == args->mods_cap) {
-		args->mods_cap = max(16, args->mods_cap * 3 / 2);
-		mods = krealloc_array(args->mods, args->mods_cap, sizeof(*mods), GFP_KERNEL);
+	if (arr->mods_cnt == arr->mods_cap) {
+		arr->mods_cap = max(16, arr->mods_cap * 3 / 2);
+		mods = krealloc_array(arr->mods, arr->mods_cap, sizeof(*mods), GFP_KERNEL);
 		if (!mods)
 			return -ENOMEM;
-		args->mods = mods;
+		arr->mods = mods;
 	}
 
-	if (!try_module_get(mod))
-		return -EINVAL;
-
-	args->mods[args->mods_cnt] = mod;
-	args->mods_cnt++;
+	arr->mods[arr->mods_cnt] = mod;
+	arr->mods_cnt++;
 	return 0;
 }
 
+static bool has_module(struct modules_array *arr, struct module *mod)
+{
+	int i;
+
+	for (i = arr->mods_cnt - 1; i >= 0; i--) {
+		if (arr->mods[i] == mod)
+			return true;
+	}
+	return false;
+}
+
 static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u32 addrs_cnt)
 {
-	struct module_addr_args args = {
-		.addrs     = addrs,
-		.addrs_cnt = addrs_cnt,
-	};
-	int err;
+	struct modules_array arr = {};
+	u32 i, err = 0;
+
+	for (i = 0; i < addrs_cnt; i++) {
+		struct module *mod;
+
+		preempt_disable();
+		mod = __module_address(addrs[i]);
+		/* Either no module or we it's already stored  */
+		if (!mod || has_module(&arr, mod)) {
+			preempt_enable();
+			continue;
+		}
+		if (!try_module_get(mod))
+			err = -EINVAL;
+		preempt_enable();
+		if (err)
+			break;
+		err = add_module(&arr, mod);
+		if (err) {
+			module_put(mod);
+			break;
+		}
+	}
 
 	/* We return either err < 0 in case of error, ... */
-	err = module_kallsyms_on_each_symbol(module_callback, &args);
 	if (err) {
-		kprobe_multi_put_modules(args.mods, args.mods_cnt);
-		kfree(args.mods);
+		kprobe_multi_put_modules(arr.mods, arr.mods_cnt);
+		kfree(arr.mods);
 		return err;
 	}
 
 	/* or number of modules found if everything is ok. */
-	*mods = args.mods;
-	return args.mods_cnt;
+	*mods = arr.mods;
+	return arr.mods_cnt;
 }
 
 int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
@@ -2857,13 +2865,6 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 		       bpf_kprobe_multi_cookie_cmp,
 		       bpf_kprobe_multi_cookie_swap,
 		       link);
-	} else {
-		/*
-		 * We need to sort addrs array even if there are no cookies
-		 * provided, to allow bsearch in get_modules_for_addrs.
-		 */
-		sort(addrs, cnt, sizeof(*addrs),
-		       bpf_kprobe_multi_addrs_cmp, NULL);
 	}
 
 	err = get_modules_for_addrs(&link->mods, addrs, cnt);

kernel/trace/ftrace.c

@@ -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;
 }
 

tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c

@@ -322,7 +322,7 @@ static bool symbol_equal(long key1, long key2, void *ctx __maybe_unused)
 	return strcmp((const char *) key1, (const char *) key2) == 0;
 }
 
-static int get_syms(char ***symsp, size_t *cntp)
+static int get_syms(char ***symsp, size_t *cntp, bool kernel)
 {
 	size_t cap = 0, cnt = 0, i;
 	char *name = NULL, **syms = NULL;
@@ -349,8 +349,9 @@ static int get_syms(char ***symsp, size_t *cntp)
 	}
 
 	while (fgets(buf, sizeof(buf), f)) {
-		/* skip modules */
-		if (strchr(buf, '['))
+		if (kernel && strchr(buf, '['))
+			continue;
+		if (!kernel && !strchr(buf, '['))
 			continue;
 
 		free(name);
@@ -404,7 +405,7 @@ error:
 	return err;
 }
 
-void serial_test_kprobe_multi_bench_attach(void)
+static void test_kprobe_multi_bench_attach(bool kernel)
 {
 	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
 	struct kprobe_multi_empty *skel = NULL;
@@ -415,7 +416,7 @@ void serial_test_kprobe_multi_bench_attach(void)
 	char **syms = NULL;
 	size_t cnt = 0, i;
 
-	if (!ASSERT_OK(get_syms(&syms, &cnt), "get_syms"))
+	if (!ASSERT_OK(get_syms(&syms, &cnt, kernel), "get_syms"))
 		return;
 
 	skel = kprobe_multi_empty__open_and_load();
@@ -453,6 +454,14 @@ cleanup:
 	}
 }
 
+void serial_test_kprobe_multi_bench_attach(void)
+{
+	if (test__start_subtest("kernel"))
+		test_kprobe_multi_bench_attach(true);
+	if (test__start_subtest("modules"))
+		test_kprobe_multi_bench_attach(false);
+}
+
 void test_kprobe_multi_test(void)
 {
 	if (!ASSERT_OK(load_kallsyms(), "load_kallsyms"))