Messages in this thread | | | Subject | Re: + generic-ipi-fix-the-race-between-generic_smp_call_function_-and-hotplug_cfd.patch added to -mm tree | From | Suresh Siddha <> | Date | Sun, 20 Sep 2009 20:11:22 -0700 |
| |
On Sun, 2009-09-20 at 19:55 -0700, Xiao Guangrong wrote: > > Suresh Siddha wrote: > > On Wed, 2009-09-16 at 20:00 -0700, Xiao Guangrong wrote: > >> How about manual check/handle pending IPI interruption in the CPU context? > >> like this: > >> --- a/kernel/cpu.c > >> +++ b/kernel/cpu.c > >> @@ -173,6 +173,9 @@ static int __ref take_cpu_down(void *_param) > >> struct take_cpu_down_param *param = _param; > >> int err; > >> > >> + generic_smp_call_function_interrupt(); > >> + generic_smp_call_function_single_interrupt(); > >> + > > > > At this place, how will you ensure that the smp_call_function initiated > > by this dying cpu has reached and got serviced at its destination? > > > > Suresh, sorry for my poor English, Do you mean that how we ensure it has > pending IPI request in the dying cpu? > > generic_smp_call_function_*() will check it, if the cpu has pending request, > then handle it, else directly return. >
I am referring to the missing csd_lock_wait() here that you had in the first version of your patch. Let's say, if cpu X is going offline, we need to ensure that the smp_call_function() initiated by cpu X (i.e., smp_call_function IPI sent to some other cpu's from cpu X) got serviced before cpu X goes offline. We can't do csd_lock_wait() here, as that might deadlock (as all the other cpu's are already in stop machine with interrupts disabled).
> > All the other cpu's have disabled interrupts in the stop machine state > > by the time we come here and we can't wait. > > > > Why we can't wait? It manual check/handle the pending IPI request not wait > interruption happen. > > It not has race here because all cpu's interruption is disabled, and it not > make stop machine slow because only the dying cpu can enter take_cpu_down(), > we just wait the dying cpu handle it's pending request. > > Am I misunderstand something? > > Thanks, > Xiao >
| |