Re: signal: break out of wait loops on kthread_stop()

[Jason A. Donenfeld]

On Wed, Oct 19, 2022 at 10:00 AM Jason A. Donenfeld <Jason@xxxxxxxxx> wrote:
>
> On Wed, Oct 19, 2022 at 7:31 AM Tvrtko Ursulin
> <tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
> >
> >
> > Hi,
> >
> > A question regarding a7c01fa93aeb ("signal: break out of wait loops on
> > kthread_stop()") if I may.
> >
> > We have a bunch code in i915, possibly limited to self tests (ie debug
> > builds) but still important for our flows, which spawn kernel threads
> > and exercises parts of the driver.
> >
> > Problem we are hitting with this patch is that code did not really need
> > to be signal aware until now. Well to say that more accurately - we were
> > able to test the code which is normally executed from userspace, so is
> > signal aware, but not worry about -ERESTARTSYS or -EINTR within the test
> > cases itself.
> >
> > For example threads which exercise an internal API for a while until the
> > parent calls kthread_stop. Now those tests can hit unexpected errors.
> >
> > Question is how to best approach working around this change. It is of
> > course technically possible to rework our code in more than one way,
> > although with some cost and impact already felt due reduced pass rates
> > in our automated test suites.
> >
> > Maybe an opt out kthread flag from this new behavior? Would that be
> > acceptable as a quick fix? Or any other comments?
>
> You can opt out by running `clear_tsk_thread_flag(current,
> TIF_NOTIFY_SIGNAL);` at the top of your kthread. But you should really
> fix your code instead. Were I your reviewer, I wouldn't merge code
> that took the lazy path like that. However, that should work, if you
> do opt for the quick fix.

Oh my, I haven't had my coffee yet and sent that too fast without
thinking straight. That certainly won't work as intended. Sorry for
the noise.

Jason