[PATCH bpf-next v2 2/9] bpf: refactor the modules_array to ptr_array

[Menglong Dong]

Refactor the struct modules_array to more general struct ptr_array, which
is used to store the pointers.

Meanwhiles, introduce the bpf_try_add_ptr(), which checks the existing of
the ptr before adding it to the array.

Seems it should be moved to another files in "lib", and I'm not sure where
to add it now, and let's move it to kernel/bpf/syscall.c for now.

Signed-off-by: Menglong Dong <dongmenglong.8 at bytedance.com>
---
 include/linux/bpf.h      | 10 +++++++++
 kernel/bpf/syscall.c     | 37 +++++++++++++++++++++++++++++++
 kernel/trace/bpf_trace.c | 48 ++++++----------------------------------
 3 files changed, 54 insertions(+), 41 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 0f677fdcfcc7..997765cdf474 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -304,6 +304,16 @@ struct bpf_map {
 	s64 __percpu *elem_count;
 };
 
+struct ptr_array {
+	void **ptrs;
+	int cnt;
+	int cap;
+};
+
+int bpf_add_ptr(struct ptr_array *arr, void *ptr);
+bool bpf_has_ptr(struct ptr_array *arr, struct module *mod);
+int bpf_try_add_ptr(struct ptr_array *arr, void *ptr);
+
 static inline const char *btf_field_type_name(enum btf_field_type type)
 {
 	switch (type) {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f63f4da4db5e..4f230fd1f8e4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -479,6 +479,43 @@ static void bpf_map_release_memcg(struct bpf_map *map)
 }
 #endif
 
+int bpf_add_ptr(struct ptr_array *arr, void *ptr)
+{
+	void **ptrs;
+
+	if (arr->cnt == arr->cap) {
+		arr->cap = max(16, arr->cap * 3 / 2);
+		ptrs = krealloc_array(arr->ptrs, arr->cap, sizeof(*ptrs), GFP_KERNEL);
+		if (!ptrs)
+			return -ENOMEM;
+		arr->ptrs = ptrs;
+	}
+
+	arr->ptrs[arr->cnt] = ptr;
+	arr->cnt++;
+	return 0;
+}
+
+bool bpf_has_ptr(struct ptr_array *arr, struct module *mod)
+{
+	int i;
+
+	for (i = arr->cnt - 1; i >= 0; i--) {
+		if (arr->ptrs[i] == mod)
+			return true;
+	}
+	return false;
+}
+
+int bpf_try_add_ptr(struct ptr_array *arr, void *ptr)
+{
+	if (bpf_has_ptr(arr, ptr))
+		return -EEXIST;
+	if (bpf_add_ptr(arr, ptr))
+		return -ENOMEM;
+	return 0;
+}
+
 static int btf_field_cmp(const void *a, const void *b)
 {
 	const struct btf_field *f1 = a, *f2 = b;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 241ddf5e3895..791e97a3f8e3 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2873,43 +2873,9 @@ static void symbols_swap_r(void *a, void *b, int size, const void *priv)
 	}
 }
 
-struct modules_array {
-	struct module **mods;
-	int mods_cnt;
-	int mods_cap;
-};
-
-static int add_module(struct modules_array *arr, struct module *mod)
-{
-	struct module **mods;
-
-	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;
-		arr->mods = mods;
-	}
-
-	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 modules_array arr = {};
+	struct ptr_array arr = {};
 	u32 i, err = 0;
 
 	for (i = 0; i < addrs_cnt; i++) {
@@ -2918,7 +2884,7 @@ static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u3
 		preempt_disable();
 		mod = __module_address(addrs[i]);
 		/* Either no module or we it's already stored  */
-		if (!mod || has_module(&arr, mod)) {
+		if (!mod || bpf_has_ptr(&arr, mod)) {
 			preempt_enable();
 			continue;
 		}
@@ -2927,7 +2893,7 @@ static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u3
 		preempt_enable();
 		if (err)
 			break;
-		err = add_module(&arr, mod);
+		err = bpf_add_ptr(&arr, mod);
 		if (err) {
 			module_put(mod);
 			break;
@@ -2936,14 +2902,14 @@ static int get_modules_for_addrs(struct module ***mods, unsigned long *addrs, u3
 
 	/* We return either err < 0 in case of error, ... */
 	if (err) {
-		kprobe_multi_put_modules(arr.mods, arr.mods_cnt);
-		kfree(arr.mods);
+		kprobe_multi_put_modules((struct module **)arr.ptrs, arr.cnt);
+		kfree(arr.ptrs);
 		return err;
 	}
 
 	/* or number of modules found if everything is ok. */
-	*mods = arr.mods;
-	return arr.mods_cnt;
+	*mods = (struct module **)arr.ptrs;
+	return arr.cnt;
 }
 
 static int addrs_check_error_injection_list(unsigned long *addrs, u32 cnt)
-- 
2.39.2