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Subject: Re: [PATCH] cpufreq: check OF /cpus presence before dereferencing it
From: Viresh Kumar <viresh.kumar@linaro.org>
To: Paolo Pisati <paolo.pisati@canonical.com>
Cc: cpufreq@vger.kernel.org, "Rafael J. Wysocki" <rjw@sisk.pl>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
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On Wed, Mar 27, 2013 at 9:02 PM, Paolo Pisati
<paolo.pisati@canonical.com> wrote:
> check for '/cpus' presence before blindly dereferencing it:
>
> [    4.181793] Unable to handle kernel NULL pointer dereference at virtual address 0000001c
> [    4.181793] pgd = c0004000
> [    4.181823] [0000001c] *pgd=00000000
> [    4.181823] Internal error: Oops: 5 [#1] SMP ARM
> [    4.181823] Modules linked in:
> [    4.181823] CPU: 1    Tainted: G        W     (3.8.0-15-generic #25~hbankD)
> [    4.181854] PC is at of_get_next_child+0x64/0x70
> [    4.181854] LR is at of_get_next_child+0x24/0x70
> [    4.181854] pc : [<c04fda18>]    lr : [<c04fd9d8>]    psr: 60000113
> [    4.181854] sp : ed891ec0  ip : ed891ec0  fp : ed891ed4
> [    4.181884] r10: c04dafd0  r9 : c098690c  r8 : c0936208
> [    4.181884] r7 : ed890000  r6 : c0a63d00  r5 : 00000000  r4 : 00000000
> [    4.181884] r3 : 00000000  r2 : 00000000  r1 : 00000000  r0 : c0b2acc8
> [    4.181884] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
> [    4.181884] Control: 10c5387d  Table: adcb804a  DAC: 00000015
> [    4.181915] Process swapper/0 (pid: 1, stack limit = 0xed890238)
> [    4.181915] Stack: (0xed891ec0 to 0xed892000)
> [    4.181915] 1ec0: c09b7b70 00000007 ed891efc ed891ed8 c04daff4 c04fd9c0 00000000 c09b7b70
> [    4.181915] 1ee0: 00000007 c0a63d00 ed890000 c0936208 ed891f54 ed891f00 c00088e0 c04dafdc
> [    4.181945] 1f00: ed891f54 ed891f10 c006e940 00000000 00000000 00000007 00000007 c08a4914
> [    4.181945] 1f20: 00000000 c07dbd30 c0a63d00 c09b7b70 00000007 c0a63d00 000000bc c0936208
> [    4.181945] 1f40: c098690c c0986914 ed891f94 ed891f58 c0936a40 c00087bc 00000007 00000007
> [    4.181976] 1f60: c0936208 be8bda20 b6eea010 c0a63d00 c064547c 00000000 00000000 00000000
> [    4.181976] 1f80: 00000000 00000000 ed891fac ed891f98 c0645498 c09368c8 00000000 00000000
> [    4.181976] 1fa0: 00000000 ed891fb0 c0014658 c0645488 00000000 00000000 00000000 00000000
> [    4.182006] 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> [    4.182006] 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
> [    4.182037] [<c04fda18>] (of_get_next_child+0x64/0x70) from [<c04daff4>] (cpu0_cpufreq_driver_init+0x24/0x284)
> [    4.182067] [<c04daff4>] (cpu0_cpufreq_driver_init+0x24/0x284) from [<c00088e0>] (do_one_initcall+0x130/0x1b0)
> [    4.182067] [<c00088e0>] (do_one_initcall+0x130/0x1b0) from [<c0936a40>] (kernel_init_freeable+0x184/0x24c)
> [    4.182098] [<c0936a40>] (kernel_init_freeable+0x184/0x24c) from [<c0645498>] (kernel_init+0x1c/0xf4)
> [    4.182128] [<c0645498>] (kernel_init+0x1c/0xf4) from [<c0014658>] (ret_from_fork+0x14/0x20)
> [    4.182128] Code: f57ff04f e320f004 e89da830 e89da830 (e595001c)
> [    4.182128] ---[ end trace 634903a22e8609cb ]---
> [    4.182189] Kernel panic - not syncing: Attempted to kill init!  exitcode=0x0000000b
> [    4.182189]
> [    4.642395] CPU0: stopping
>
> Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
> ---
>  drivers/cpufreq/cpufreq-cpu0.c |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq-cpu0.c b/drivers/cpufreq/cpufreq-cpu0.c
> index 4e5b7fb..f3e8f51 100644
> --- a/drivers/cpufreq/cpufreq-cpu0.c
> +++ b/drivers/cpufreq/cpufreq-cpu0.c
> @@ -178,10 +178,16 @@ static struct cpufreq_driver cpu0_cpufreq_driver = {
>
>  static int cpu0_cpufreq_probe(struct platform_device *pdev)
>  {
> -       struct device_node *np;
> +       struct device_node *np, *tmp;
>         int ret;
>
> -       for_each_child_of_node(of_find_node_by_path("/cpus"), np) {
> +       tmp = of_find_node_by_path("/cpus");
> +       if (!tmp) {
> +               pr_err("failed to find OF /cpus\n");
> +               return -ENOENT;
> +       }
> +
> +       for_each_child_of_node(tmp, np) {
>                 if (of_get_property(np, "operating-points", NULL))
>                         break;
>         }

Just do: s/tmp/parent

and add

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