Re: [PATCH v2 2/2] cpuidle: Validate cpu_dev in cpuidle_add_sysfs

[Rafael J. Wysocki]

On Thu, Mar 23, 2017 at 4:22 PM, Vaidyanathan Srinivasan
<svaidy@xxxxxxxxxxxxxxxxxx> wrote:
> If a given cpu is not in cpu_present and cpu hotplug
> is disabled, arch can skip setting up the cpu_dev.
>
> Arch cpuidle driver should pass correct cpu mask
> for registration, but failing to do so by the driver
> causes error to propagate and crash like this:
>
> [   30.076045] Unable to handle kernel paging request for
>                                 data at address 0x00000048
> [   30.076100] Faulting instruction address: 0xc0000000007b2f30
> cpu 0x4d: Vector: 300 (Data Access) at [c000003feb18b670]
>     pc: c0000000007b2f30: kobject_get+0x20/0x70
>     lr: c0000000007b3c94: kobject_add_internal+0x54/0x3f0
>     sp: c000003feb18b8f0
>    msr: 9000000000009033
>    dar: 48
>  dsisr: 40000000
>   current = 0xc000003fd2ed8300
>   paca    = 0xc00000000fbab500   softe: 0        irq_happened: 0x01
>     pid   = 1, comm = swapper/0
> Linux version 4.11.0-rc2-svaidy+ (sv@sagarika) (gcc version 6.2.0
> 20161005 (Ubuntu 6.2.0-5ubuntu12) ) #10 SMP Sun Mar 19 00:08:09 IST 2017
> enter ? for help
> [c000003feb18b960] c0000000007b3c94 kobject_add_internal+0x54/0x3f0
> [c000003feb18b9f0] c0000000007b43a4 kobject_init_and_add+0x64/0xa0
> [c000003feb18ba70] c000000000e284f4 cpuidle_add_sysfs+0xb4/0x130
> [c000003feb18baf0] c000000000e26038 cpuidle_register_device+0x118/0x1c0
> [c000003feb18bb30] c000000000e26c48 cpuidle_register+0x78/0x120
> [c000003feb18bbc0] c00000000168fd9c powernv_processor_idle_init+0x110/0x1c4
> [c000003feb18bc40] c00000000000cff8 do_one_initcall+0x68/0x1d0
> [c000003feb18bd00] c0000000016242f4 kernel_init_freeable+0x280/0x360
> [c000003feb18bdc0] c00000000000d864 kernel_init+0x24/0x160
> [c000003feb18be30] c00000000000b4e8 ret_from_kernel_thread+0x5c/0x74
>
> Validating cpu_dev fixes the crash and reports correct error message like:
>
> [   30.163506] Failed to register cpuidle device for cpu136
> [   30.173329] Registration of powernv driver failed.
>
> Signed-off-by: Vaidyanathan Srinivasan <svaidy@xxxxxxxxxxxxxxxxxx>

The previous version is in linux-next already and I'm going to push it
for merging shortly.

> ---
>  drivers/cpuidle/sysfs.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
> index c5adc8c..f2c3bce 100644
> --- a/drivers/cpuidle/sysfs.c
> +++ b/drivers/cpuidle/sysfs.c
> @@ -615,6 +615,18 @@ int cpuidle_add_sysfs(struct cpuidle_device *dev)
>         struct device *cpu_dev = get_cpu_device((unsigned long)dev->cpu);
>         int error;
>
> +       /*
> +        * Return error if cpu_device is not setup for this cpu.  This
> +        * could happen if arch did not setup cpu_device since this
> +        * cpu is not in cpu_present mask and the driver did not send
> +        * correct cpu mask at registration.  Without this check we
> +        * would end up passing bogus value for &cpu_dev->kobj in
> +        * kobject_init_and_add().
> +        */
> +
> +       if (!cpu_dev)
> +               return -ENODEV;
> +
>         kdev = kzalloc(sizeof(*kdev), GFP_KERNEL);
>         if (!kdev)
>                 return -ENOMEM;
> --
> 2.9.3
>