linux-kernel - Re: [PATCH 1/3] RISC-V: Do not wait indefinitely in __cpu

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Message-ID: <CAAhSdy3Wd6tPrv-XDqETK8sBetYSg-mjHzZXJQJgUFeufEjPfA@mail.gmail.com>
Date:   Thu, 27 Dec 2018 09:06:24 +0530
From:   Anup Patel <anup@...infault.org>
To:     Atish Patra <atish.patra@....com>
Cc:     linux-riscv@...ts.infradead.org, Albert Ou <aou@...s.berkeley.edu>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Dmitriy Cherkasov <dmitriy@...-tech.org>,
        Jason Cooper <jason@...edaemon.net>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Michael Clark <michaeljclark@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Patrick Stählin <me@...ki.ch>,
        Rob Herring <robh@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Damien Le Moal <Damien.LeMoal@....com>
Subject: Re: [PATCH 1/3] RISC-V: Do not wait indefinitely in __cpu_up

On Thu, Dec 27, 2018 at 4:39 AM Atish Patra <atish.patra@....com> wrote:
>
> In SMP path, __cpu_up waits for other CPU to come online
> indefinitely. This is wrong as other CPU might be disabled
> in machine mode and possible CPU is set to the cpus present
> in DT.
>
> Introduce a completion variable and waits only for a second.
>
> Signed-off-by: Atish Patra <atish.patra@....com>
> ---
>  arch/riscv/kernel/smpboot.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index 18cda0e8..bb8cd242 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -39,6 +39,7 @@
>
>  void *__cpu_up_stack_pointer[NR_CPUS];
>  void *__cpu_up_task_pointer[NR_CPUS];
> +static DECLARE_COMPLETION(cpu_running);
>
>  void __init smp_prepare_boot_cpu(void)
>  {
> @@ -77,6 +78,7 @@ void __init setup_smp(void)
>
>  int __cpu_up(unsigned int cpu, struct task_struct *tidle)
>  {
> +       int ret = 0;
>         int hartid = cpuid_to_hartid_map(cpu);
>         tidle->thread_info.cpu = cpu;
>
> @@ -92,10 +94,15 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
>                   task_stack_page(tidle) + THREAD_SIZE);
>         WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
>
> -       while (!cpu_online(cpu))
> -               cpu_relax();
> +       wait_for_completion_timeout(&cpu_running,
> +                                           msecs_to_jiffies(1000));
>
> -       return 0;
> +       if (!cpu_online(cpu)) {
> +               pr_crit("CPU%u: failed to come online\n", cpu);
> +               ret = -EIO;
> +       }
> +
> +       return ret;
>  }
>
>  void __init smp_cpus_done(unsigned int max_cpus)
> @@ -121,6 +128,7 @@ asmlinkage void __init smp_callin(void)
>          * a local TLB flush right now just in case.
>          */
>         local_flush_tlb_all();
> +       complete(&cpu_running);
>         /*
>          * Disable preemption before enabling interrupts, so we don't try to
>          * schedule a CPU that hasn't actually started yet.
> --
> 2.7.4
>

Looks good to me.

Reviewed-by: Anup Patel <anup@...infault.org>