On Sat, Jan 08, 2022 at 12:35:40PM -0600, Eric W. Biederman wrote: > 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(). > > Some of those users of the now removed thread_exit() in staging are > among the offenders. > > However thread_exit() was implemented as: > #define thread_exit() complete_and_exit(NULL, 0) > > Which does nothing with a completion, it was just a really funny way to > spell "do_exit(0)". Yes. And there's a plenty of cargo-culting in that area. > While I agree digging through all of the kernel threads and finding the > ones that should be calling complete_and_exit is a fine idea. It is > a concern independent of these patches. BTW, could somebody explain how could this /* * Prevent the kthread exits directly, and make sure when kthread_stop() * is called to stop a kthread, it is still alive. If a kthread might be * stopped by CACHE_SET_IO_DISABLE bit set, wait_for_kthread_stop() is * necessary before the kthread returns. */ static inline void wait_for_kthread_stop(void) { while (!kthread_should_stop()) { set_current_state(TASK_INTERRUPTIBLE); schedule(); } } in drivers/md/bcache/bcache.h possibly avoid losing wakeups? AFAICS, it can be called while in TASK_RUNNING. Suppose kthread_stop() gets called just after the check for kthread_should_stop(). Our thread is still in TASK_RUNNING; kthread_stop() sets the flag for the next kthread_should_stop() to observe and does wake_up_process() to our thread. Which does nothing. Now our thread goes into TASK_INTERRUPTIBLE and calls schedule(). Sure, as soon as it gets woken up it'll call kthread_should_stop(), get true from it and that's it. What's going to wake it up, though? The same goes for e.g. fs/btrfs/disk-io.c:cleaner_kthread(): if (kthread_should_stop()) return 0; if (!again) { set_current_state(TASK_INTERRUPTIBLE); schedule(); __set_current_state(TASK_RUNNING); } can't be right. Similar fun exists in e.g. fs/jfs, etc. Am I missing something?