在看內核log時,發現有一個misc_register註冊失敗的warning。一開始以爲配置的參數有誤,看代碼也使用了參數MISC_DYNAMIC_MINOR,不太可能出現註冊失敗的情況。
int misc_register(struct miscdevice * misc)
{
dev_t dev;
int err = 0;
bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
if (is_dynamic) {
struct miscdevice *c;
int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
if (i >= DYNAMIC_MINORS) {
err = -EBUSY;
goto out;
}
list_for_each_entry(c, &misc_list, list) {
if (c == misc) {
err = -EEXIST;
goto out;
}
}
misc->minor = DYNAMIC_MINORS - i - 1;
set_bit(i, misc_minors);
} else {
...
}
...
}
加打印發現is_dynamic爲0,但有使用參數MISC_DYNAMIC_MINOR,不應該爲0。出問題的代碼如下,能看出哪裏有問題沒
static int xxx_img_probe(struct platform_device *pdev)
{
int ret = 0;
ret = misc_register(&image_dev);
if (ret) {
pr_err("cannot register miscdev on minor=%d (%d).\n",IMAGE_MINOR, ret);
ret = -EACCES;
goto exit;
}
}
static const struct of_device_id of_match_table_dcam[] = {
{ .compatible = "xxx,dcam"},
};
static struct platform_driver xxx_img_driver = {
.probe = xxx_img_probe,
.driver = {
.of_match_table = of_match_ptr(of_match_table_dcam),
},
};
發現xxx_img_probe跑了兩遍,第一次註冊成功了,導致misc->minor爲固定值(非255),導致不能動態註冊該設備,使用靜態註冊時,該設備號已經被使用了,從而註冊失敗。
但xxx_img_probe爲什麼會跑兩遍的,設備只有一個。一開始以爲xxx_img_probe返回值爲EPROBE_DEFER,導致xxx_img_probe再次運行。但打印發現xxx_img_probe返回值爲0。只能加打印進行跟蹤了。
const struct of_device_id *__of_match_node(const struct of_device_id *matches,
const struct device_node *node)
{
const struct of_device_id *best_match = NULL;
int score, best_score = 0;
if (!matches)
return NULL;
for (; matches->name[0] || matches->type[0] || matches->compatible[0]; matches++) {
score = __of_device_is_compatible(node, matches->compatible,
matches->type, matches->name);
if (score > best_score) {
best_match = matches;
best_score = score;
}
}
return best_match;
}
發現matches指向了其他的非法數據結構,導致probe函數第二次運行。
static const struct of_device_id of_match_table_dcam[] = {
{ .compatible = "xxx,dcam"},
+ { },
};
罪魁禍首就是少了一個括號,導致野指針出現,出現了非法probe。這是某cpu廠商代碼的bug,已提給他們修復。