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Date:   Mon, 15 Apr 2019 14:21:28 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Dexuan Cui <decui@microsoft.com>
Cc:     "tglx@linutronix.de" <tglx@linutronix.de>,
        "riel@surriel.com" <riel@surriel.com>,
        "jpoimboe@redhat.com" <jpoimboe@redhat.com>,
        "luto@kernel.org" <luto@kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        "marcelo.cerri@canonical.com" <marcelo.cerri@canonical.com>,
        "apw@canonical.com" <apw@canonical.com>,
        "olaf@aepfle.de" <olaf@aepfle.de>, vkuznets <vkuznets@redhat.com>,
        "jasowang@redhat.com" <jasowang@redhat.com>
Subject: Re: [PATCH] smp: Do not warn if smp_call_function_single() is doing
 a self call.
Message-ID: <20190415122128.GO11158@hirez.programming.kicks-ass.net>
References: <20190412235341.29379-1-decui@microsoft.com>
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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?