linux-kernel - RE: [PATCH] smp: Do not warn if smp_call_function

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Message-ID: <PU1P153MB01693370A9E788356ACF989BBF250@PU1P153MB0169.APCP153.PROD.OUTLOOK.COM>
Date:   Wed, 17 Apr 2019 23:50:33 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        vkuznets <vkuznets@...hat.com>
CC:     "riel@...riel.com" <riel@...riel.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "luto@...nel.org" <luto@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        "marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
        "apw@...onical.com" <apw@...onical.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: RE: [PATCH] smp: Do not warn if smp_call_function_single() is doing a
 self call.

> From: Thomas Gleixner <tglx@...utronix.de>
> Sent: Tuesday, April 16, 2019 1:13 PM
> > ...
> > True. And before we start digging deeper into this, let's step back: why
> > do we need to do clockevents_unbind_device() on hybernation? Can we just
> > disable the device and re-enable it back on resume?

We do clockevents_unbind_device as part of hv_synic_cleanup(), which is
called as a CPU hotplug callback: see vmbus_bus_init():
    ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "hyperv/vmbus:online",
                        hv_synic_init, hv_synic_cleanup);

Yes, it looks the right thing is to implement the suspend/resume callbacks of
the clock_event_device. Thank you for the suggestion! I'll look into this.

> Yes. That's the right thing to do. Simple solution is to implement the
> suspend/resume callbacks on the clock events device and be done with it.

Agreed.

> > Actually, all usages of clockevents_unbind_device() in kernel are
> > limited to Hyper-V and with Michael's patches moving this out of VMBus
> > driver I think it can go away completely.

Thanks for the heads-up! I'll rebase to Michael's patches.
 
> Correct. There was a driver which required that, but that's gone by now and
> of course nobody noticed that it was the last user. The reason why this
> exists was to allow switching out an active clocksource similar to the
> sysfs unbind file but without user space interaction.
> 
> 	tglx

Thanks for the background sharing!

- Dexuan