From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: KVM: protect concurrent make_all_cpus_request
Date: Wed, 17 Jun 2009 18:52:02 +0200
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References: <20090617135347.GC14583@amt.cnet>
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Cc: kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
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On Wed, Jun 17, 2009 at 10:53:47AM -0300, Marcelo Tosatti wrote:
> 
> 
> make_all_cpus_request contains a race condition which can 
> trigger false request completed status, as follows:
> 
> CPU0                                              CPU1
> 
> if (test_and_set_bit(req,&vcpu->requests))
>    ....                                        	   if (test_and_set_bit(req,&vcpu->requests))
>    ..                                                  return
> proceed to smp_call_function_many(wait=1)
> 
> Use a spinlock to serialize concurrent CPUs.

Agreed, this is the safest...