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    SubjectRe: [RFC PATCH 09/10] POWERPC: smp: remove call to ipi_call_lock()/ipi_call_unlock()
    On Tue, May 29, 2012 at 03:16:04PM +0800, Yong Zhang wrote:
    > From: Yong Zhang <yong.zhang@windriver.com>
    >
    > 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.

    Thanx, Paul

    > Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
    > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    > Cc: Paul Mackerras <paulus@samba.org>
    > Cc: linuxppc-dev@lists.ozlabs.org
    > ---
    > 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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