Date: Fri, 2 Nov 2007 12:10:10 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-acpi@freebsd.org Cc: Glen <glen.leeder@nokia.com> Subject: Re: SMP system shutdown hang (acpi_cpu_shutdown - smp_rendezvous) Message-ID: <200711021210.11259.jhb@freebsd.org> In-Reply-To: <472AA11F.3080302@root.org> References: <472A53B2.6030901@nokia.com> <472AA11F.3080302@root.org>
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On Friday 02 November 2007 12:01:35 am Nate Lawson wrote: > 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. > > > > I noticed a few threads relating to this and have already tried stuff > > like changing kern.sched.ipiwakeup.enabled & machdep.cpu_idle_hlt. > > Neither had any effect. > > > > 1) I tried removing the call to smp_rendezvous in acpi_cpu_shutdown and > > this stops the hang from happening. Does anyone know the purpose of this > > call in the shutdown code or if I might suffer some consequence by > > removing it? > > I have one more thing I needed to consider. There's a race where a > thread could be entering acpi_cpu_idle() to read a C2-3 register but > that register state gets destroyed with the softc before the read. In > that case, I thought there could be a panic, hence why I originally put > in the smp_rendezvous(). However, I don't think device_shutdown() frees > softcs (need to look in the newbus code to be sure). So I still should > be able to remove this code after checking more closely. It does not. Only detach does. -- John Baldwin
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