Re: [PATCH V3] cpufreq: fix a NULL pointer dereference triggered by _PPC changed notification

[Viresh Kumar]

On 18 December 2014 at 11:58, Ethan Zhao <ethan.zhao@xxxxxxxxxx> wrote:
> If _PPC changed notification happens before governor was initiated while kernel
> is booting, a NULL pointer dereference will be triggered:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000030
>  IP: [<ffffffff81470453>] __cpufreq_governor+0x23/0x1e0
>  PGD 0
>  Oops: 0000 [#1] SMP
>  ... ...
>  RIP: 0010:[<ffffffff81470453>]  [<ffffffff81470453>]
>  __cpufreq_governor+0x23/0x1e0
>  RSP: 0018:ffff881fcfbcfbb8  EFLAGS: 00010286
>  RAX: 0000000000000000 RBX: ffff881fd11b3980 RCX: ffff88407fc20000
>  RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff881fd11b3980
>  RBP: ffff881fcfbcfbd8 R08: 0000000000000000 R09: 000000000000000f
>  R10: ffffffff818068d0 R11: 0000000000000043 R12: 0000000000000004
>  R13: 0000000000000000 R14: ffffffff8196cae0 R15: 0000000000000000
>  FS:  0000000000000000(0000) GS:ffff881fffc00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000030 CR3: 00000000018ae000 CR4: 00000000000407f0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>  Process kworker/0:3 (pid: 750, threadinfo ffff881fcfbce000, task
>  ffff881fcf556400)
>  Stack:
>   ffff881fffc17d00 ffff881fcfbcfc18 ffff881fd11b3980 0000000000000000
>   ffff881fcfbcfc08 ffffffff81470d08 ffff881fd11b3980 0000000000000007
>   ffff881fcfbcfc18 ffff881fffc17d00 ffff881fcfbcfd28 ffffffff81472e9a
>  Call Trace:
>   [<ffffffff81470d08>] __cpufreq_set_policy+0x1b8/0x2e0
>   [<ffffffff81472e9a>] cpufreq_update_policy+0xca/0x150
>   [<ffffffff81472f20>] ? cpufreq_update_policy+0x150/0x150
>   [<ffffffff81324a96>] acpi_processor_ppc_has_changed+0x71/0x7b
>   [<ffffffff81320bcd>] acpi_processor_notify+0x55/0x115
>   [<ffffffff812f9c29>] acpi_device_notify+0x19/0x1b
>   [<ffffffff813084ca>] acpi_ev_notify_dispatch+0x41/0x5f
>   [<ffffffff812f64a4>] acpi_os_execute_deferred+0x27/0x34
>
> The root cause is a race conditon -- cpufreq core and acpi-cpufreq driver
> were initiated, but cpufreq_governor wasn't and _PPC changed notification
> happened, __cpufreq_governor() was called within acpi_os_execute_deferred
> kernel thread context.
>
> To fix this panic issue, add pointer checking code in __cpufreq_governor()
> before pointer policy->governor is to be dereferenced.
>
> Signed-off-by: Ethan Zhao <ethan.zhao@xxxxxxxxxx>
> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
>  v2&v3: correct comment style.
>
>  drivers/cpufreq/cpufreq.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 4473eba..b75735c 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2021,6 +2021,11 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
>         /* Don't start any governor operations if we are entering suspend */
>         if (cpufreq_suspended)
>                 return 0;
> +       /*
> +        * Governor might not be initiated here if _PPC changed notification
> +        * happened, check it.
> +        */
> +       if (!policy->governor)
> +               return -EINVAL;
>
>         if (policy->governor->max_transition_latency &&
>             policy->cpuinfo.transition_latency >

It will take me sometime to get cpufreq core simplified, till that time

Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>

to yet another band-aid :)
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