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

[Jason A. Donenfeld]

Hi Sebastian,

On 8/1/22, Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:
> 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.

CONFIG_PROVE_RAW_LOCK_NESTING catches RT issues on non-RT. It doesn't
catch non-RT issues. So lockdep isn't actually warning about something
real as far as non-RT is concerned when CONFIG_PROVE_RAW_LOCK_NESTING
is enabled.

So probably this v4 patch should expand that condition to be:

IS_ENABLED(CONFIG_PROVE_RAW_LOCK_NESTING) || IS_ENABLED(CONFIG_PREEMPT_RT)

That's somewhat distasteful, I realize, but it *does* make the code
actually match reality, which is maybe better.

Jason