linux-kernel - Re: [PATCH v5 31/45] blackfin/smp: Use get/put_online_cpus

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Message-ID: <CAA_GA1fSLNKSDTGSzHoA+j-mur85BvoSRkARq+DMfORuwrrX4Q@mail.gmail.com>
Date:	Mon, 28 Jan 2013 17:09:34 +0800
From:	Bob Liu <lliubbo@...il.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	rostedt@...dmis.org, wangyun@...ux.vnet.ibm.com,
	xiaoguangrong@...ux.vnet.ibm.com, rjw@...k.pl, sbw@....edu,
	fweisbec@...il.com, linux@....linux.org.uk,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 31/45] blackfin/smp: Use get/put_online_cpus_atomic()
 to prevent CPU offline

On Tue, Jan 22, 2013 at 3:41 PM, Srivatsa S. Bhat
<srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> Once stop_machine() is gone from the CPU offline path, we won't be able to
> depend on preempt_disable() or local_irq_disable() to prevent CPUs from
> going offline from under us.
>
> Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline,
> while invoking from atomic context.
>
> Cc: Mike Frysinger <vapier@...too.org>
> Cc: Bob Liu <lliubbo@...il.com>
> Cc: Steven Miao <realmz6@...il.com>
> Cc: uclinux-dist-devel@...ckfin.uclinux.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Thanks, will be applied to my blackfin arch tree.

> ---
>
>  arch/blackfin/mach-common/smp.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/blackfin/mach-common/smp.c b/arch/blackfin/mach-common/smp.c
> index bb61ae4..6cc6d7a 100644
> --- a/arch/blackfin/mach-common/smp.c
> +++ b/arch/blackfin/mach-common/smp.c
> @@ -194,6 +194,7 @@ void send_ipi(const struct cpumask *cpumask, enum ipi_message_type msg)
>         struct ipi_data *bfin_ipi_data;
>         unsigned long flags;
>
> +       get_online_cpus_atomic();
>         local_irq_save(flags);
>         smp_mb();
>         for_each_cpu(cpu, cpumask) {
> @@ -205,6 +206,7 @@ void send_ipi(const struct cpumask *cpumask, enum ipi_message_type msg)
>         }
>
>         local_irq_restore(flags);
> +       put_online_cpus_atomic();
>  }
>
>  void arch_send_call_function_single_ipi(int cpu)
> @@ -238,13 +240,13 @@ void smp_send_stop(void)
>  {
>         cpumask_t callmap;
>
> -       preempt_disable();
> +       get_online_cpus_atomic();
>         cpumask_copy(&callmap, cpu_online_mask);
>         cpumask_clear_cpu(smp_processor_id(), &callmap);
>         if (!cpumask_empty(&callmap))
>                 send_ipi(&callmap, BFIN_IPI_CPU_STOP);
>
> -       preempt_enable();
> +       put_online_cpus_atomic();
>
>         return;
>  }
>
> --
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-- 
Regards,
--Bob
--
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