svn commit: r221703 - in head/sys: amd64/include i386/include x86/isa x86/x86

[John Baldwin]

On 5/12/11 6:55 AM, Stanislav Sedov wrote:
> On Thu, 12 May 2011 13:43:58 +0300
> Andriy Gapon<avg at FreeBSD.org>  mentioned:
>
>>
>> Theory:
>> - smp_rv_waiters[2] becomes equal to smp_rv_ncpus
>> - [at least] one slave CPU is still in the last call to cpu_spinwait() in
>> smp_rendezvous_action()
>> - master CPU notices that the condition is true, exits smp_rendezvous_cpus() and
>> calls it again
>> - the slave CPU is still in spinwait
>> - the master CPU resets smp_rv_waiters[2] to zero
>> - the slave CPU exits spinwait, see smp_rv_waiters[2] with zero value
>> - endless loop
>>
>
> That might explain it.
> Do you have a patch for me to try?
>
> Thanks!
>

The NetApp folks working on BHyVe also ran into this.  They have a fix 
that I think sounds reasonable which is to add a generation count to the 
smp rendezvous "structure" and have waiting CPUs stop waiting if the 
generation count changes.

-- 
John Baldwin