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

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2022-08-01 15:44:12 [+0200], Jason A. Donenfeld wrote:
> Hey again,
Hi Jason,

> By the way, another option that would be fine with me would be to make
> random.c use all raw spinlocks. From a non-RT perspective, that wouldn't
> change the codegen at all, so it doesn't make a huge difference to me.
> From an RT perspective, it would presumably fix a lot of these issues,
> and enable randomness to be available in any context, which is maybe
> what we want anyway. From an RT-safety point of view, I suspect doing
> this might actually be okay, because the locks are only ever protecting
> operations that are fixed duration CPU-bound, like generating a chacha
> block or something, not waiting for some I/O.
> 
> Thoughts on that?

That random-core change regarding random numbers broke lockdep, kasan (I
think) and now printk's %p. Each one of them appears to be exceptional
since we don't have _that_ many users asking for random numbers in
atomic context.
Making the locks raw would indeed solve all the issues at once. Last
time I was looking into this, would include three locks and I tried to
trigger the worst-case via "re-seed" and this was visible back then.
After the rework you did back thinks looked good.

> Jason

Sebastian