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

[Chen, Tiejun]

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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