SMP system shutdown hang (acpi_cpu_shutdown - smp_rendezvous)

[Nate Lawson]

Glen wrote:
> Hi,
> 
> I have been seeing intermittent hangs in the acpi shutdown code on a
> Intel 2.4GHz 8 CPU system. I am running a with a  Freebsd6.1 code base
> but cannot see a reason why this can't happen in other Freebsd versions.
> The hang is very irregular, I am recreating it using an expect script
> that repeatedly reboots the system. Sometimes, I can do up to 200
> reboots before observing the hang, sometimes, it happens after 5-20
> reboots.
> 
> It has been difficult to pin down the hang as the system is not
> responding to NMI events but using breakpoints I believe the hang is in 
> acpi_cpu.c:acpi_cpu_shutdown with the call to smp_rendezvous.
> 
> My theory is that one of the CPUs does not respond to ipi_all_but_self
> and that all the other CPUs are waiting for it in smp_rendezvous_action.
> The smp_rv_waiters[0] < mp_ncpus condition never gets met and the system
> hangs. This maybe happen due to other activity (or a deadlock?) on that
> CPU.

Fix committed, I'll do my best to get it into 7.0 and 6.3.

-- 
Nate