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

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Message-ID: <20190415122128.GO11158@hirez.programming.kicks-ass.net>
Date:   Mon, 15 Apr 2019 14:21:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "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>, vkuznets <vkuznets@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>
Subject: Re: [PATCH] smp: Do not warn if smp_call_function_single() is doing
 a self call.

On Fri, Apr 12, 2019 at 11:53:57PM +0000, Dexuan Cui wrote:
> If smp_call_function_single() is calling the function for itself, it's safe
> to run with irqs_disabled() == true.
> 
> I hit the warning because I'm in the below path in the .suspend callback of
> a "syscore_ops" to support hibernation for a VM running on Hyper-V:
> 
>   hv_synic_cleanup() ->
>     clockevents_unbind_device() ->
>       clockevents_unbind() ->
>         smp_call_function_single().
> 
> When the .suspend callback runs, only CPU0 is online and irqs_disabled() is
> true.

Pray tell, how well do you think mutex_lock() works with interrupts
disabled?