记录一次驱动调试过程_comm: tainted-优快云博客

本文链接：https://blog.youkuaiyun.com/m0_71275596/article/details/135325946

文章讲述了开发者在使用Exynos4412开发板进行4-bitLED模拟实验时遇到的内核警告问题，涉及gpiod_free函数在模块卸载时未正确释放GPIO资源。经过分析，发现是由于GPIO请求操作有效但释放操作提前执行导致的。解决方案是修正goto操作，确保资源释放的正确顺序。

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在开发板Exynos4412上用4个led：LED2~5来模拟4bit数实验：

seg_led_drv.c

问题：

在卸载模块时，虽然没有崩溃，但是内核打印如下警告：

[ 3494.595000] WARNING: CPU: 2 PID: 1277 at drivers/gpio/gpiolib.c:1556 gpiod_free+0xc0/0xe8() //问题出现在内核文件gpiolib.c下gpiod_free+0xc0（第1556行）

[ 3494.595000] Modules linked in: seg_led_drv(O-) [last unloaded: seg_led_drv]

[ 3494.595000] CPU: 2 PID: 1277 Comm: rmmod Tainted: G W O 3.14.0 #8

[ 3494.595000] [] (unwind_backtrace) from [] (show_stack+0x10/0x14)

[ 3494.595000] [] (show_stack) from [] (dump_stack+0x64/0xb4)

[ 3494.595000] [] (dump_stack) from [] (warn_slowpath_common+0x68/0x88)

[ 3494.595000] [] (warn_slowpath_common) from [] (warn_slowpath_null+0x1c/0x24)

[ 3494.595000] [] (warn_slowpath_null) from [] (gpiod_free+0xc0/0xe8)

[ 3494.595000] [] (gpiod_free) from [] (free_gpio+0xf4/0x14c [seg_led_drv]) //驱动程序中seg_remove()下的free_gpio()函数调用了内核中的gpiod_free()函数

[ 3494.595000] [] (free_gpio [seg_led_drv]) from [] (seg_remove+0x2c/0x68 [seg_led_drv])

[ 3494.595000] [] (seg_remove [seg_led_drv]) from [] (platform_drv_remove+0x14/0x18)

[ 3494.685000] [] (platform_drv_remove) from [] (__device_release_driver+0x58/0xb4)

[ 3494.685000] [] (__device_release_driver) from [] (driver_detach+0xac/0xb0)

[ 3494.685000] [] (driver_detach) from [] (bus_remove_driver+0x4c/0x90)

[ 3494.685000] [] (bus_remove_driver) from [] (SyS_delete_module+0x124/0x180)

[ 3494.685000] [] (SyS_delete_module) from [] (ret_fast_syscall+0x0/0x30)

[ 3494.685000] ---[ end trace d371ea0a334f660f ]---

分析过程：

从打印信息可以看出：

1、当卸载驱动模块时，seg_remove中的释放gpio的操作（free_gpio ()）出现了问题

2、问题根源在内核文件gpiolib.c的第1556行，查看该文件下包含1556行的函数，

1525 static void gpiod_free(struct gpio_desc *desc)
1526 {
1527     unsigned long       flags;
1528     struct gpio_chip    *chip;
1529 
1530     might_sleep();
1531 
1532     if (!desc) {
1533         WARN_ON(extra_checks);
1534         return;
1535     }
1536 
1537     gpiod_unexport(desc);
1538 
1539     spin_lock_irqsave(&gpio_lock, flags);
1540 
1541     chip = desc->chip;
1542     if (chip && tes