linux-kernel - Re: [PATCH 1/2] sched/idle: Fix arch_cpu

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Message-ID: <yt9dh7p54u50.fsf@linux.ibm.com>
Date:   Tue, 01 Dec 2020 12:56:27 +0100
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Guenter Roeck <linux@...ck-us.net>, rafael@...nel.org,
        viresh.kumar@...aro.org, mingo@...nel.org, x86@...nel.org,
        mark.rutland@....com, will@...nel.org,
        linux-kernel@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-s390@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] sched/idle: Fix arch_cpu_idle() vs tracing

Hi Peter,

Peter Zijlstra <peterz@...radead.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