作者liptonbin (我還存在耶)
看板C_and_CPP
標題[問題] 請問free分配空間的概念
時間Fri Apr 21 11:02:55 2023
請教一下兩個問題，如下
為什麼path分配空間後,最後面寫kfree(path)會導致crash,這樣寫法是錯的嗎?
另外code寫free_token = token,然後最後kfree(free_token),為什麼要多寫一個指標去free?
謝謝
int test(struct device *dev, const char *p_i8_buf, size_t count)
{
int i32_ret = 0;
char *temp_buf, *token, *path;
char *free_temp_buf, *free_token;
unsigned long fun = 0;
const char *delim = " ,";
temp_buf = kzalloc(RAYDIUM_FW_BIN_PATH_LENGTH + 1, GFP_KERNEL);
if (temp_buf == NULL)
{
return -ENOMEM;
}
token = kzalloc(RAYDIUM_FW_BIN_PATH_LENGTH + 1, GFP_KERNEL);
if (token == NULL) {
kfree(temp_buf);
return -ENOMEM;
}
path = kzalloc(RAYDIUM_FW_BIN_PATH_LENGTH + 1, GFP_KERNEL);
if (path == NULL) {
kfree(temp_buf);
kfree(token);
return -ENOMEM;
}
free_token = token;
free_temp_buf = temp_buf;
strlcpy(temp_buf, p_i8_buf, count);
token = strsep(&temp_buf, delim);
if(token == NULL)
{
kfree(free_token);
kfree(free_temp_buf);
kfree(path);
return -EINVAL;
}
i32_ret = kstrtoul(token, 16, &fun);
if (i32_ret < 0) {
kfree(free_token);
kfree(free_temp_buf);
kfree(path);
return i32_ret;
}
path = strsep(&temp_buf, delim);//log path
parse(dev, fun, path);
kfree(free_token);
kfree(free_temp_buf);
//kfree(path); //will not crash <-----------------
or kfree(path); //will crash<------------------------
return count;
}
crash log:
[ 1316.983483] Unable to handle kernel paging request at virtual address 00005e00
[ 1316.990498] pgd = db59c000
[ 1316.993168] [00005e00] *pgd=00000000
[ 1316.996642] Internal error: Oops: 5 [#1] PREEMPT SMP ARM
[ 1317.001840] Modules linked in: drmboot(P) mali_kbase
[ 1317.006705] CPU: 3 PID: 1326 Comm: sh Tainted: P 3.10.0 #6612
[ 1317.013355] task: db702a00 ti: db728000 task.ti: db728000
[ 1317.018648] PC is at kmem_cache_alloc_trace+0x7c/0x1c0
[ 1317.023676] LR is at test+0x98/0x2fc
[ 1317.028707] pc : [<c0100620>] r : [<c04b39a8>] sr: 20010013
[ 1317.028707] sp : db729eb0 p : 00000000 p : 00000101
[ 1317.039960] r10: 00000f53 9 : 01328000 8 : c04b39a8
2.
通常看到都是寫法3,
我在看很多別人寫的code的寫法都是1,請問是不是改成2才對？
if(!handle)等價if(handle==NULL)嗎？
謝謝回答
struct input_handle *handle;
(1) handle = kzalloc(sizeof(*handle), GFP_KERNEL);
if (!handle)
return -ENOMEM;
(2)
handle = kzalloc(sizeof(*handle), GFP_KERNEL);
if (!handle)
{
kfree(handle);
return -ENOMEM;
}
(3)
handle = kzalloc(sizeof(*handle), GFP_KERNEL);
if (handle == NULL)
{
return -ENOMEM;
}
kfree(handle);
-----
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1F：推 Schottky: 問題出在 strsep 那一行，你 kfree() 的 path 不是當初 04/21 13:24
2F：→ Schottky: kzalloc() 出來的位址 04/21 13:25
3F：推 gusion: 你的path在strsep那行被更新了，變成指到temp_buf裡面的某 04/21 13:25
4F：→ gusion: 個位置，不是原本kzalloc出來的那塊，所以最後kfree(path) 04/21 13:25
5F：→ Schottky: 還有 code 麻煩縮排一下，我還要用 indent 縮排過才看得 04/21 13:25
6F：→ gusion: 才會出錯，另外沒有kfree(path)，原本allocate的memory就 04/21 13:25
7F：→ gusion: 沒人free，也會memory leak 04/21 13:25
8F：→ Schottky: 懂你在寫什麼 04/21 13:25
9F：推 gusion: 另外，error handling我是習慣在尾巴加上label，用goto 04/21 13:28
10F：→ lycantrope: 2-(2)應該是拿槍射自己腳吧ww 04/21 17:48