Messages in this thread | | | Date | Thu, 8 Jul 2021 00:35:23 +1000 | Subject | Re: [tip: sched/core] sched/core: Initialize the idle task with preemption disabled | From | Alexey Kardashevskiy <> |
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On 08/07/2021 00:14, Guenter Roeck wrote: > On 7/7/21 5:11 AM, Valentin Schneider wrote: >> On 07/07/21 14:03, Frederic Weisbecker wrote: >>> On Wed, Jul 07, 2021 at 12:55:20AM +0100, Valentin Schneider wrote: >>>> Thanks for the report. >>>> >>>> So somehow the init task ends up with a non-zero preempt_count()? Per >>>> FORK_PREEMPT_COUNT we should exit __ret_from_fork() with a zero >>>> count, are >>>> you hitting the WARN_ONCE() in finish_task_switch()? >>>> >>>> Does CONFIG_DEBUG_PREEMPT=y yield anything interesting? >>>> >>>> I can't make sense of this right now, but it's a bit late :) I'll >>>> grab some >>>> toolchain+qemu tomorrow and go poke at it (and while at it I need to >>>> do the >>>> same with powerpc). >>> >>> One possible issue is that s390's init_idle_preempt_count() doesn't >>> apply on the >>> target idle task but on the _current_ CPU. And since smp_init() -> >>> idle_threads_init() is actually called remotely, we are overwriting >>> the current >>> CPU preempt_count() instead of the target one. >> >> Indeed, this becomes quite obvious when tracing the preemption count >> changes. This also means that s390 relied on the idle_thread_get() >> from the >> hotplug machinery to properly setup the preempt count, rather than >> init_idle_preempt_count() - which is quite yuck. >> >> I'll write a patch for that and likely one for powerpc. >> > > Can you reproduce the problem with a powerpc qemu emulation ? > If so, how do you reproduce it there ? Reason for asking is that I don't > see > the problem with any of my powerpc emulations, and I would like to add test > case(s) if possible.
I can reproduce the problem on powerpc easily - qemu with "-smp 2" does it.
-- Alexey
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