On Thu, 22 Aug 2015 00:21:00 -0000, Valdis Kletnieks said:
Sounds like a reference counting problem.
As far as I know, reference counter for line discipline sets to 0 in tty_register_ldisc(), increases to 1 in get_ldops() and decreases to 1 in put_ldops(). In tty_unregister_ldisc() it checks this value and if the reference counter > 0, it returns error -EBUSY And please advice how could I transfer data between kernel and user space not using filp_open() and filp_close(). 2015-08-22 0:21 GMT+03:00 <Valdis.Kletnieks@vt.edu>:
On Thu, 13 Aug 2015 13:00:58 -0000, Margarita Glushkin said:
I have a linux kernel driver for serial device, which uses line discipline and char device. Driver works with all old kernels, starting from 3.8 this driver still works, but when I unload it and load again to the memory (modprobe -r bpsctl_mod, after modprobe bpsctl_mod), it crashes the kernel. It can't unregister line discipline, because this line discipline is busy.
Sounds like a reference counting problem. When your line discipline is busy, somebody should have a reference on the module so it can't be unloaded. I don't see any such reference taking/freeing in your posted code.
Your crash is almost certainly because you're unloading it out from under active use, which will probably result in somebody overlaying storage. Frankly, you're probably lucky the system lives long enough for you to reload it.....
Oh, and filp_open() is usually the wrong way to solve whatever problem you were trying to solve by using it.