Commit 6a5f2d6e authored by Jiri Olsa's avatar Jiri Olsa Committed by Alexei Starovoitov
Browse files

bpf: Change modules resolving for kprobe multi link 



We currently use module_kallsyms_on_each_symbol that iterates all
modules/symbols and we try to lookup each such address in user
provided symbols/addresses to get list of used modules.

This fix instead only iterates provided kprobe addresses and calls
__module_address on each to get list of used modules. This turned
out to be simpler and also bit faster.

On my setup with workload (executed 10 times):

   # test_progs -t kprobe_multi_bench_attach/modules

Current code:

 Performance counter stats for './test.sh' (5 runs):

    76,081,161,596      cycles:k                   ( +-  0.47% )

           18.3867 +- 0.0992 seconds time elapsed  ( +-  0.54% )

With the fix:

 Performance counter stats for './test.sh' (5 runs):

    74,079,889,063      cycles:k                   ( +-  0.04% )

           17.8514 +- 0.0218 seconds time elapsed  ( +-  0.12% )

Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Reviewed-by: default avatarZhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230116101009.23694-4-jolsa@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent edac4b5b

kernel/trace/bpf_trace.c

+47 −46
Original line number Diff line number Diff line
@@ -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(NULL, 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);