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: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230116101009.23694-4-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 095f7f8..8124f1a 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/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(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);