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    SubjectRe: [PATCH 1/2] sched/idle: Fix arch_cpu_idle() vs tracing
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    Hi Peter,

    Peter Zijlstra <peterz@infradead.org> writes:

    > On Mon, Nov 30, 2020 at 01:00:03PM -0800, Guenter Roeck wrote:
    >> On Fri, Nov 20, 2020 at 12:41:46PM +0100, Peter Zijlstra wrote:
    >> > We call arch_cpu_idle() with RCU disabled, but then use
    >> > local_irq_{en,dis}able(), which invokes tracing, which relies on RCU.
    >> >
    >> > Switch all arch_cpu_idle() implementations to use
    >> > raw_local_irq_{en,dis}able() and carefully manage the
    >> > lockdep,rcu,tracing state like we do in entry.
    >> >
    >> > (XXX: we really should change arch_cpu_idle() to not return with
    >> > interrupts enabled)
    >> >
    >>
    >> Has this patch been tested on s390 ? Reason for asking is that it causes
    >> all my s390 emulations to crash. Reverting it fixes the problem.
    >
    > My understanding is that it changes the error on s390. Previously it
    > would complain about the local_irq_enable() in arch_cpu_idle(), now it
    > complains when taking an interrupt during idle.

    I looked into adding the required functionality for s390, but the code
    we would need to add to entry.S is rather large - as you noted we would
    have to duplicate large portions of irqentry_enter() into our code.
    Given that s390 was fine before that patch, can you revert it and submit
    it again during the next merge window?

    Thanks
    Sven

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