David Laight <David.Laight@xxxxxxxxxx> writes: > From: Eric W. Biederman >> Sent: 08 January 2022 18:36 >> >> Al Viro <viro@xxxxxxxxxxxxxxxxxx> writes: >> >> > IMO the right way to handle that would be >> > 1) turn these two do_exit() into do_exit(0), to reduce >> > confusion >> > 2) deal with all do_exit() in kthread payloads. Your >> > name for the primitive is fine, IMO. >> > 3) make that primitive pass the return value by way of >> > a field in struct kthread, adjusting kthread_stop() accordingly >> > and passing 0 to do_exit() in kthread_exit() itself. >> > >> > (2) is not as trivial as you seem to hope, though. Your patches >> > in drivers/staging/rt*/ had papered over the problem in there, >> > but hadn't really solved it. >> > >> > thread_exit() should've been shot, all right, but it really ought >> > to have been complete_and_exit() there. The thing is, complete() >> > + return does *not* guarantee that driver won't get unloaded before >> > the thread terminates. Possibly freeing its .code and leaving >> > a thread to resume running in there as soon as it regains CPU. >> > >> > The point of complete_and_exit() is that it's noreturn *and* in >> > core kernel. So it can be safely used in a modular kthread, >> > if paired with wait_for_completion() in or before module_exit. >> > complete() + do_exit() (or complete + return as you've gotten >> > there) doesn't give such guarantees at all. >> >> >> I think we are mostly in agreement here. >> >> There are kernel threads started by modules that do: >> complete(...); >> return 0; >> >> That should be at a minimum calling complete_and_exit. Possibly should >> be restructured to use kthread_stop(). > > There is also module_put_and_exit(0); > Which must have an implied THIS_MODULE. Later in the patch series I change module_put_and_exit -> module_put_and_kthread_exit complete_and_exit -> complete_and_kthread_exit The problem that I understand all was seeing was where people should have been using complete_and_exit and were not. Eric
