Re: [PATCH v2] random: do crng pre-init loading in worker rather than irq

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

On 2022-02-24 16:29:37 [+0100], Jason A. Donenfeld wrote:
> Taking spinlocks from IRQ context is problematic for PREEMPT_RT. That
> is, in part, why we take trylocks instead. But apparently this still
> trips up various lock dependency analyzers. That seems like a bug in the
> analyzers that should be fixed, rather than having to change things
> here.

Could you please post a lockdep report so I can take a look?

> But maybe there's another reason to change things up: by deferring the
> crng pre-init loading to the worker, we can use the cryptographic hash
> function rather than xor, which is perhaps a meaningful difference when
> considering this data has only been through the relatively weak
> fast_mix() function.
> 
> The biggest downside of this approach is that the pre-init loading is
> now deferred until later, which means things that need random numbers
> after interrupts are enabled, but before workqueues are running -- or
> before this particular worker manages to run -- are going to get into
> trouble. Hopefully in the real world, this window is rather small,
> especially since this code won't run until 64 interrupts had occurred.
> 
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Eric Biggers <ebiggers@kernel.org>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Other than that:

Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Sebastian