kref_put , kernel object ref and release

問題出現在 usb-serial 上，當 suspend 時 device suspend -- disconnect
當 resume 時， 重新 probe。

結果.. 有些跳過順序： # first boot -- 0.1.2.3 # suspend and resume -- 0.1.3.4 跳過 2

發現 disconect 時，call usb_serial_put( )，
void usb_serial_put(struct usb_serial *serial) { kref_put(&serial->kref, destroy_serial); }

call 的就是 kref_put( ):
/** * kref_put - decrement refcount for object. * @kref: object. * @release: pointer to the function that will clean up the object when the * last reference to the object is released. * This pointer is required, and it is not acceptable to pass kfree * in as this function. * * Decrement the refcount, and if 0, call release(). * Return 1 if the object was removed, otherwise return 0. Beware, if this * function returns 0, you still can not count on the kref from remaining in * memory. Only use the return value if you want to see if the kref is now * gone, not present. */ int kref_put(struct kref *kref, void (*release)(struct kref *kref)) { WARN_ON(release == NULL); WARN_ON(release == (void (*)(struct kref *))kfree); if (atomic_dec_and_test(&kref->refcount)) { release(kref); return 1; } return 0; }

也就是 decrease refcount, 如果是 0, 就 call 傳進來的 function : release()

參考 kref_get( ) , 在 usb-serial port 有人 open 時，就會呼叫。
也就是說，一定要所有 open 的人都 close 了， refcount 才會是 0