On 2/24/22, Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> wrote: > 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? What exactly is the difference you see mattering in the order? I keep chasing my tail trying to think about it. Jason
