linux-kernel - Re: [tip: sched/core] x86, sched: Add support for frequency invariance

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Date:   Tue, 31 Mar 2020 20:11:25 +0200
From:   Giovanni Gherdovich <ggherdovich@...e.cz>
To:     Chris Wilson <chris@...is-wilson.co.uk>,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        tip-bot2 for Giovanni Gherdovich <tip-bot2@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Doug Smythies <dsmythies@...us.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        x86 <x86@...nel.org>
Subject: Re: [tip: sched/core] x86, sched: Add support for frequency
 invariance

On Mon, 2020-03-30 at 12:05 +0100, Chris Wilson wrote:
> Quoting tip-bot2 for Giovanni Gherdovich (2020-01-29 11:32:58)
> > The following commit has been merged into the sched/core branch of tip:
> > 
> > Commit-ID:     1567c3e3467cddeb019a7b53ec632f834b6a9239
> > Gitweb:        https://git.kernel.org/tip/1567c3e3467cddeb019a7b53ec632f834b6a9239
> > Author:        Giovanni Gherdovich <ggherdovich@...e.cz>
> > AuthorDate:    Wed, 22 Jan 2020 16:16:12 +01:00
> > Committer:     Ingo Molnar <mingo@...nel.org>
> > CommitterDate: Tue, 28 Jan 2020 21:36:59 +01:00
> > [...]
>
> Since this has become visible via linux-next [20200326?], we have been
> deluged by oops during cpu-hotplug.
> 
> <6> [184.949219] [IGT] perf_pmu: starting subtest cpu-hotplug
> <4> [185.092279] IRQ 24: no longer affine to CPU0
> <4> [185.092285] IRQ 25: no longer affine to CPU0
> <6> [185.093709] smpboot: CPU 0 is now offline
> <6> [186.107062] smpboot: Booting Node 0 Processor 0 APIC 0x0
> <3> [186.107643] BUG: sleeping function called from invalid context at ./include/linux/percpu-rwsem.h:49
> <3> [186.107648] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 0, name: swapper/0
> [...]
> 
> repeating ad nauseam, e.g.
> https://intel-gfx-ci.01.org/tree/linux-next/next-20200327/shard-hsw4/dmesg9.txt
> 
> Across all our test boxen.
> -Chris

Hello Chris,

thank you for catching this problem and sorry for the mess.

Until your message I wasn't aware that CPU0 can be hotplugged, but now that I
check the feature is been there since v3.8 :/

The code assumes cpu0 is always there and I need to fix that.

It seems your report comes from executing an automated test suite, can you
give me a link to the test sources and a hint on how to run it? I'd like to
reproduce locally so that I make sure I correctly address this problem.

Thanks,
Giovanni