On Fri, Mar 12, 2021 at 1:17 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I'm _guessing_ it's just that now those threads are user threads, and
> then the freezing logic expects them to freeze/thaw using a signal
> machinery or something like that. And that doesn't work when there is
> no signal handling for those threads.
IOW, I think it's this logic in freeze_task():
if (!(p->flags & PF_KTHREAD))
fake_signal_wake_up(p);
else
wake_up_state(p, TASK_INTERRUPTIBLE);
where that "not a PF_KTHREAD" test will trigger for the io_uring
threads, and it does that fake_signal_wake_up(), and then
signal_wake_up() does that
set_tsk_thread_flag(t, TIF_SIGPENDING);
but the io_uring thread has no way to react to it.
So now the io_uring thread will see "I have pending signals" (even if
there is no actual pending signal - it's just a way to get normal
processes to get out of TASK_INTERRUPTIBLE and return to user space
handling).
And the pending fake signal will never go away, because there is no
"return to user space" handling.
So I think the fix is to simply make freeze_task() not do that fake
signal thing for IO-uring threads either.
Linus
