Am Thu, Feb 10, 2022 at 07:04:20PM +0100 schrieb Sebastian Andrzej Siewior: > > @@ -999,9 +1016,10 @@ void add_interrupt_randomness(int irq) > > > > fast_mix(fast_pool); > > add_interrupt_bench(cycles); > > + new_count = ++fast_pool->count; > > > > if (unlikely(crng_init == 0)) { > > - if ((fast_pool->count >= 64) && > > + if (new_count >= 64 && > > crng_fast_load((u8 *)fast_pool->pool, sizeof(fast_pool->pool)) > 0) { > > crng_fast_load() does spin_trylock_irqsave() in hardirq context. It does > not produce any warning on RT but is still wrong IMHO: > - lockdep will see a random task and I remember in the past it produced > strange lock chains based on this. > > - Should another task attempt to acquire this lock then it will PI-boost the > wrong task. > > If we just could move this, too. > > I don't know how timing critical this is but the first backtrace from > crng_fast_load() came (to my surprise) from hwrng_fillfn() (a kthread) > and added 64bytes in one go. That's a hw rng (such as a tpm chip or the virtio-rng driver) providing some entropy; if it's 64 bytes of input, crng_init progresses to 1, and crng_fast_load() should never be called again.[*] I'm a bit suprised that the hw_rng input occurred so early (it's only at device_initcall() level), and earlier than 64 interrupts. But that may differ from system to system. Note that crng_fast_load() will also never be called from add_interrupt_randomness() if EFI, DT or kexec provides bootloader entropy of at least 64 bytes, and CONFIG_RANDOM_TRUST_BOOTLOADER is set and/or CONFIG_RANDOM_TRUST_CPU is set and the RDRAND/RDSEED instructions do not fail. If neither of these three conditions (hw_rng is run early, bootloader or CPU randomness) are met, the initial and early seeding of the base_crng depends on add_interrupt_randomness(), and should happen rather quickly. > I did move that crng_fast_load() into the worker and did made some > numbers: > <idle>-0 [000] d..h1.. 2.069924: add_interrupt_randomness: Tick > > first interrupt > … > swapper/0-1 [000] d..h.11 2.341938: add_interrupt_randomness: Tick > swapper/0-1 [000] d..h.11 2.341938: add_interrupt_randomness: work > > the 64th interrupt, scheduling the worker. > > swapper/0-1 [000] d..h.11 2.345937: add_interrupt_randomness: Tick > swapper/0-1 [000] d..h111 2.349938: add_interrupt_randomness: Tick > swapper/0-1 [000] d..h.11 2.353939: add_interrupt_randomness: Tick > swapper/0-1 [000] d..h.11 2.357940: add_interrupt_randomness: Tick > swapper/0-1 [000] d..h111 2.361939: add_interrupt_randomness: Tick > swapper/0-1 [000] d..h111 2.365939: add_interrupt_randomness: Tick > swapper/0-1 [000] d..h.11 2.369941: add_interrupt_randomness: Tick > kworker/0:0H-6 [000] ....... 2.384714: mix_interrupt_randomness: load > kworker/0:0H-6 [000] ....... 2.384715: crng_fast_load: 16 > <idle>-0 [001] dn.h1.. 3.205766: add_interrupt_randomness: Tick > <idle>-0 [019] dn.h1.. 6.771047: add_interrupt_randomness: Tick > > 7 interrupts got lost before the worker could run & load first 16 bytes. > The workqueue core gets initialized at that point and spawns first > worker. So the reason for the longer delay here is that the workqueue core had not been initialized beforehand? > After that the interrupts took a break. > And then the work-to-load delay was quite low: > > <idle>-0 [019] dn.h1.. 7.586234: add_interrupt_randomness: Tick > <idle>-0 [019] dn.h1.. 7.586234: add_interrupt_randomness: work > kworker/19:0H-175 [019] ....... 7.586504: mix_interrupt_randomness: load > kworker/19:0H-175 [019] ....... 7.586507: crng_fast_load: 16 > <idle>-0 [020] dn.h1.. 7.614649: add_interrupt_randomness: Tick > <idle>-0 [020] dn.h1.. 7.614651: add_interrupt_randomness: work > <idle>-0 [020] dn.h1.. 7.614736: add_interrupt_randomness: Tick > kworker/20:0H-183 [020] dn.h... 7.614859: add_interrupt_randomness: Tick > kworker/20:0H-183 [020] ....... 7.614871: mix_interrupt_randomness: load > kworker/20:0H-183 [020] ....... 7.614872: crng_fast_load: 16 > <idle>-0 [018] dn.h1.. 8.352423: add_interrupt_randomness: Tick > <idle>-0 [018] dn.h1.. 8.352423: add_interrupt_randomness: work > kworker/18:0H-167 [018] dn.h1.. 8.352438: add_interrupt_randomness: Tick > kworker/18:0H-167 [018] dn.h1.. 8.352448: add_interrupt_randomness: Tick > kworker/18:0H-167 [018] dn.h1.. 8.352459: add_interrupt_randomness: Tick > kworker/18:0H-167 [018] dn.h1.. 8.352491: add_interrupt_randomness: Tick > kworker/18:0H-167 [018] ....... 8.352505: mix_interrupt_randomness: load > kworker/18:0H-167 [018] ....... 8.352506: crng_fast_load: 16 > > In total we lost 13 ticks. Was this still way before the initramfs was up and running? > I did the same test on PREEMPT_VOLUNTARY and lost 2 ticks only. Thanks, Dominik [*] Actually, there's some contradiciton going on: If we do not trust the hw_rng device (that is, its quality setting is 0), crng_fast_load() will be called nonetheless, and the hw_rng-provided input will be used to increment crng_init to 1. If !CONFIG_RANDOM_TRUST_BOOTLOADER, only crng_slow_load() is called, and crng_init will remain at 0. Similar for !CONFIG_RANDOM_TRUST_CPU.