Am Wed, Feb 23, 2022 at 07:55:11PM +0100 schrieb Jason A. Donenfeld: > 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. > > 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: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> > Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > Cc: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Theodore Ts'o <tytso@xxxxxxx> > Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> > --- > drivers/char/random.c | 62 ++++++++++++------------------------------- > 1 file changed, 17 insertions(+), 45 deletions(-) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 536237a0f073..9fb06fc298d3 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -1298,7 +1278,12 @@ static void mix_interrupt_randomness(struct work_struct *work) > local_irq_enable(); > > mix_pool_bytes(pool, sizeof(pool)); > - credit_entropy_bits(1); > + > + if (unlikely(crng_init == 0)) > + crng_pre_init_inject(pool, sizeof(pool), true); > + else > + credit_entropy_bits(1); > + > memzero_explicit(pool, sizeof(pool)); > } Might it make sense to call crng_pre_init_inject() before mix_pool_bytes? Otherwise, all looks fine: Reviewed-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> Thanks Dominik
