Re: [PATCH v4] lib/vsprintf: defer filling siphash key on RT

[Sebastian Andrzej Siewior]

On 2022-08-01 15:36:32 [+0200], Jason A. Donenfeld wrote:
> Hi Sebastian,
Hi Jason,

> > Can have the same behaviour regardless of CONFIG_PREEMPT_RT? Here
> > lockdep _may_ yell with !RT because it is broken for RT.
> > If we agree that we drop the first %p print here, can we do this on
> > both (regardless of CONFIG_PREEMPT_RT)?
> 
> "Lockdep may yell" -- but this would be when lockdep is turned on to
> catch RT bugs, not to catch non-RT bugs. The actual bug only exists on
> RT. This is an RT problem. Stop pretending that this is a real issue
> outside of RT. It isn't. This is *only* an RT issue. So why would we
> make things worse for an issue that doesn't actually exist on non-RT?

You do remember the warning that poped up in random core with
CONFIG_PROVE_RAW_LOCK_NESTING enabled? Where I said it does not affect
!RT it just points out a RT problem in a !RT config?
If you fix this with one code path for RT and another one for !RT then
you will have this warning _if_ the caller has a raw_spinlock_t
acquired.

> I too generally prefer having only one code path and not two. But the
> way this patch is written, the worker function just gets reused with a
> straight call on the non-RT case, so it doesn't actually require
> duplicating code.

> Jason

Sebastian