On Sat, Jul 29, 2023 at 09:00:02PM -0700, Guenter Roeck wrote: > On 7/27/23 16:18, Joel Fernandes wrote: > > [ ... ] > > > > I freely confess that I am having a hard time imagining what would > > > be CPU dependent in that code. Timing, maybe? Whatever the reason, > > > I am not seeing these failures in my testing. > > > > > > So which of the following Kconfig options is defined in your .config? > > > CONFIG_TASKS_RCU, CONFIG_TASKS_RUDE_RCU, and CONFIG_TASKS_TRACE_RCU. > > > > > > If you have more than one of them, could you please apply this patch > > > and show me the corresponding console output from the resulting hang? > > > > FWIW, I am not able to repro this issue either. If a .config can be shared of the problem system, I can try it out to see if it can be reproduced on my side. > > > > I managed to bisect the problem. See bisect log below. Bisect repeated twice. > so it should be reliable. I don't really understand it, but the following > reverts fix the problem. This is on top of next-20230721 because next-20230728 > crashes immediately in my tests. > > 0caafe9b94ab (HEAD) Revert "sched/fair: Remove sched_feat(START_DEBIT)" > 518bdbd39fdb Revert "sched/fair: Add lag based placement" > a011162c3e32 Revert "sched/fair: Implement an EEVDF-like scheduling policy" > df579720bf98 Revert "sched/fair: Commit to lag based placement" > aac459a7e738 Revert "sched/smp: Use lag to simplify cross-runqueue placement" > 8d686eb173e1 Revert "sched/fair: Commit to EEVDF" > 486474c50f95 Revert "sched/debug: Rename sysctl_sched_min_granularity to sysctl_sched_base_slice" > 79e94d67d08a Revert "sched/fair: Propagate enqueue flags into place_entity()" > ae867bc97b71 (tag: next-20230721) Add linux-next specific files for 20230721 > > For context: x86 images (32 and 64 bit) in -next tend to hang at > > [ 2.309323] RCU Tasks: Setting shift to 0 and lim to 1 rcu_task_cb_adjust=1. > [ 2.311634] Running RCU-tasks wait API self tests > > The hang is not seen with every boot; it happens roughly about once every > 10 boot attempts. It is not CPU dependent as I initially thought. > > Configuration file is at http://server.roeck-us.net/qemu/x86-next/config. > Example qemu command line: Hurmph, let me see if I can reproduce on next-20230731 (not having the older next thingies around).
