linux-kernel - Re: [PATCH v2 1/2] powerpc/powernv/cpuidle: Pass correct drv->cpumask for registration

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Message-ID: <CAJZ5v0jujyxWYbUAKkzkq9ZdT476LsHLfD2S9GtwHBPQByKWUw@mail.gmail.com>
Date:   Thu, 23 Mar 2017 16:28:31 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:     Michael Neuling <mikey@...ling.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] powerpc/powernv/cpuidle: Pass correct drv->cpumask
 for registration

On Thu, Mar 23, 2017 at 4:22 PM, Vaidyanathan Srinivasan
<svaidy@...ux.vnet.ibm.com> wrote:
> drv->cpumask defaults to cpu_possible_mask in __cpuidle_driver_init().
> On PowerNV platform cpu_present could be less than cpu_possible in cases
> where firmware detects the cpu, but it is not available to the OS.  When
> CONFIG_HOTPLUG_CPU=n, such cpus are not hotplugable at runtime and hence
> we skip creating cpu_device.
>
> This breaks cpuidle on powernv where register_cpu() is not called for
> cpus in cpu_possible_mask that cannot be hot-added at runtime.
>
> Trying cpuidle_register_device() on cpu without cpu_device will cause
> crash like this:
>
> cpu 0xf: Vector: 380 (Data SLB Access) at [c000000ff1503490]
>     pc: c00000000022c8bc: string+0x34/0x60
>     lr: c00000000022ed78: vsnprintf+0x284/0x42c
>     sp: c000000ff1503710
>    msr: 9000000000009033
>    dar: 6000000060000000
>   current = 0xc000000ff1480000
>   paca    = 0xc00000000fe82d00   softe: 0        irq_happened: 0x01
>     pid   = 1, comm = swapper/8
> Linux version 4.11.0-rc2 (sv@...arika) (gcc version 4.9.4
> (Buildroot 2017.02-00004-gc28573e) ) #15 SMP Fri Mar 17 19:32:02 IST 2017
> enter ? for help
> [link register   ] c00000000022ed78 vsnprintf+0x284/0x42c
> [c000000ff1503710] c00000000022ebb8 vsnprintf+0xc4/0x42c (unreliable)
> [c000000ff1503800] c00000000022ef40 vscnprintf+0x20/0x44
> [c000000ff1503830] c0000000000ab61c vprintk_emit+0x94/0x2cc
> [c000000ff15038a0] c0000000000acc9c vprintk_func+0x60/0x74
> [c000000ff15038c0] c000000000619694 printk+0x38/0x4c
> [c000000ff15038e0] c000000000224950 kobject_get+0x40/0x60
> [c000000ff1503950] c00000000022507c kobject_add_internal+0x60/0x2c4
> [c000000ff15039e0] c000000000225350 kobject_init_and_add+0x70/0x78
> [c000000ff1503a60] c00000000053c288 cpuidle_add_sysfs+0x9c/0xe0
> [c000000ff1503ae0] c00000000053aeac cpuidle_register_device+0xd4/0x12c
> [c000000ff1503b30] c00000000053b108 cpuidle_register+0x98/0xcc
> [c000000ff1503bc0] c00000000085eaf0 powernv_processor_idle_init+0x140/0x1e0
> [c000000ff1503c60] c00000000000cd60 do_one_initcall+0xc0/0x15c
> [c000000ff1503d20] c000000000833e84 kernel_init_freeable+0x1a0/0x25c
> [c000000ff1503dc0] c00000000000d478 kernel_init+0x24/0x12c
> [c000000ff1503e30] c00000000000b564 ret_from_kernel_thread+0x5c/0x78
>
> This patch fixes the bug by passing correct cpumask from
> powernv-cpuidle driver.
>
> Signed-off-by: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>

That needs to be ACKed by someone familiar with powernv.

> ---
>  drivers/cpuidle/cpuidle-powernv.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
> index a06df51..82f7b33 100644
> --- a/drivers/cpuidle/cpuidle-powernv.c
> +++ b/drivers/cpuidle/cpuidle-powernv.c
> @@ -175,6 +175,24 @@ static int powernv_cpuidle_driver_init(void)
>                 drv->state_count += 1;
>         }
>
> +       /*
> +        * On PowerNV platform cpu_present may be less that cpu_possible in
> +        * cases where firmware detects the cpu, but it is not available to the
> +        * OS.  If CONFIG_HOTPLUG_CPU=n then such CPUs are not hotplugable at
> +        * runtime and hence cpu_devices are not created for those cpus by
> +        * generic topology_init().
> +        *
> +        * drv->cpumask defaults to cpu_possible_mask in
> +        * __cpuidle_driver_init().  This breaks cpuidle on powernv where
> +        * cpu_devices are not created for cpus in cpu_possible_mask that
> +        * cannot be hot-added later at runtime.
> +        *
> +        * Trying cpuidle_register_device() on a cpu without cpu_devices is
> +        * incorrect. Hence pass correct cpu mask to generic cpuidle driver.
> +        */
> +
> +       drv->cpumask = (struct cpumask *)cpu_present_mask;
> +
>         return 0;
>  }
>
> --
> 2.9.3
>