linux-kernel - Re: [[PATCH 2/2] kvm: enable preemption to register/unregister preempt notifier

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Message-ID: <5599CFCF.7070301@intel.com>
Date:	Mon, 06 Jul 2015 08:46:07 +0800
From:	"Chen, Tiejun" <tiejun.chen@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
CC:	linux-kernel@...r.kernel.org, Gleb Natapov <gleb@...nel.org>
Subject: Re: [[PATCH 2/2] kvm: enable preemption to register/unregister preempt
 notifier

On 2015/7/3 19:23, Paolo Bonzini wrote:
> On 03/07/2015 10:56, Tiejun Chen wrote:
>> After commit 1cde2930e154 ("sched/preempt: Add static_key() to
>> preempt_notifiers") is introduced, preempt_notifier_{register, unregister}
>> always hold a mutex, jump_label_mutex. So in current case this shouldn't
>> work further under the circumstance of disabled preemption, and its also
>> safe since we're just handling a per-vcpu stuff with holding vcpu->mutex.
>> Otherwise, some warning messages are posted like this,
>>
>> BUG: scheduling while atomic: qemu-system-x86/17177/0x00000002
>> 2 locks held by qemu-system-x86/17177:
>>   #0:  (&vcpu->mutex){+.+.+.}, at: [<ffffffffa035fb48>] vcpu_load+0x28/0xf0 [kvm]
>>   #1:  (jump_label_mutex){+.+.+.}, at: [<ffffffff81244b54>] static_key_slow_inc+0xc4/0x140
>> Modules linked in: x86_pkg_temp_thermal kvm_intel kvm
>> Preemption disabled at:[<ffffffffa035fd3e>] kvm_vcpu_ioctl+0x7e/0xeb0 [kvm]
>
> Thanks for your work Tiejun.  However, the original patch is crap.  I've
> asked to revert it.
>

Yeah, its better to revert that commit since finally this also trigger a 
bug 100671: vmwrite error in vmx_vcpu_run.

Thanks
Tiejun
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