Re: [PATCH] linux-user: un-register threads from RCU before exit

[Peter Maydell <peter.maydell@linaro.org>]

On Tue, 11 Feb 2020 at 17:36, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> Through a mechanism I don't quite yet understand we can find ourselves
> with a left over RCU thread when we exit group. This is a racy failure
> that occurs for example with:
>
>   alpha-linux-user running testthread
>     with libhowvec.so plugin
>     but only when run from make
>
> This may not be the correct fix but it seems to alleviate the
> symptoms.

This is weird. The only time we call preexit_cleanup()
is when the next thing we do is to terminate the entire
process all at once. (For some reason in one place
we do that by calling _exit() and in another place
by calling exit_group() -- I don't see why we need that
inconsistency).

I'm pretty sure the system emulation threads don't
call rcu_unregister_thread() for the "whole process
is going away" case, so something odd is happening here...

thanks
-- PMM