On Mon, Jun 18, 2012 at 10:51:59AM +0800, Yong Zhang wrote:
> On Sat, Jun 16, 2012 at 09:32:19AM -0700, Paul E. McKenney wrote:
> > On Tue, May 29, 2012 at 03:16:04PM +0800, Yong Zhang wrote:
> > > From: Yong Zhang <[email protected]>
> > >
> > > 1) call_function.lock used in smp_call_function_many() is just to protect
> > > call_function.queue and &data->refs, cpu_online_mask is outside of the
> > > lock. And it's not necessary to protect cpu_online_mask,
> > > because data->cpumask is pre-calculate and even if a cpu is brougt up
> > > when calling arch_send_call_function_ipi_mask(), it's harmless because
> > > validation test in generic_smp_call_function_interrupt() will take care
> > > of it.
> > >
> > > 2) For cpu down issue, stop_machine() will guarantee that no concurrent
> > > smp_call_fuction() is processing.
> >
> > However, there is an effort to get rid of stop_machine() from the
> > CPU-down path... So something else will be needed.
>
> Yeah. So Thomas changed the commit log like below:
> [
> ipi_call_lock/unlock() lock resp. unlock call_function.lock. This lock
> protects only the call_function data structure itself, but it's
> completely unrelated to cpu_online_mask. The mask to which the IPIs
> are sent is calculated before call_function.lock is taken in
> smp_call_function_many(), so the locking around set_cpu_online() is
> pointless and can be removed.
>
> [ tglx: Massaged changelog ]
> ]
>
> in tip/smp/hotplug.
Got it, thank you!
Thanx, Paul
> Thanks,
> Yong
>
> >
> > Thanx, Paul
> >
> > > Signed-off-by: Yong Zhang <[email protected]>
> > > Cc: Benjamin Herrenschmidt <[email protected]>
> > > Cc: Paul Mackerras <[email protected]>
> > > Cc: [email protected]
> > > ---
> > > arch/powerpc/kernel/smp.c | 2 --
> > > 1 files changed, 0 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> > > index e4cb343..e1417c4 100644
> > > --- a/arch/powerpc/kernel/smp.c
> > > +++ b/arch/powerpc/kernel/smp.c
> > > @@ -571,7 +571,6 @@ void __devinit start_secondary(void *unused)
> > > if (system_state == SYSTEM_RUNNING)
> > > vdso_data->processorCount++;
> > > #endif
> > > - ipi_call_lock();
> > > notify_cpu_starting(cpu);
> > > set_cpu_online(cpu, true);
> > > /* Update sibling maps */
> > > @@ -601,7 +600,6 @@ void __devinit start_secondary(void *unused)
> > > of_node_put(np);
> > > }
> > > of_node_put(l2_cache);
> > > - ipi_call_unlock();
> > >
> > > local_irq_enable();
> > >
> > > --
> > > 1.7.5.4
> > >
> >
> > --
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> --
> Only stand for myself
>
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