linux-kernel - Re: [PATCH] KVM: X86: Fix softlockup when get the current kvmclock timestamp

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Message-ID: <da5b8123-ca3f-5c48-75fe-b982274eed05@redhat.com>
Date:   Mon, 6 Nov 2017 11:21:09 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH] KVM: X86: Fix softlockup when get the current kvmclock
 timestamp

On 06/11/2017 11:06, Wanpeng Li wrote:
> 2017-11-06 17:29 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>> On 06/11/2017 01:55, Wanpeng Li wrote:
>>> This can be reproduced when running kvm-unit-tests/hyperv_stimer.flat and
>>> cpu-hotplug stress simultaneously. kvm_get_time_scale() takes too long which
>>> results in softlockup.
>>
>> Apart from the pr_debug, kvm_get_time_scale should take less than a
>> microsecond.  The patch is fine, but can you confirm that pr_debug is
>> the culprit?
> 
> I can still encounter softlockup after removing the pr_debug.

Is kvm_get_time_scale getting into an infinite loop then?  That would be
the actual bug.

Paolo