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From:   Chunyan Zhang <zhang.lyra@gmail.com>
Date:   Tue, 21 Nov 2017 16:57:46 +0800
Message-ID: <CAAfSe-s9qbRXBMZGbAuWXqhFr4Bt9LSv6=uvYCUW+UhdpcNKcg@mail.gmail.com>
Subject: Re: [PATCH] clk: fix a panic error caused by accessing NULL pointer
To:     Stephen Boyd <sboyd@codeaurora.org>
Cc:     Chunyan Zhang <chunyan.zhang@spreadtrum.com>,
        Michael Turquette <mturquette@baylibre.com>,
        linux-clk <linux-clk@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Cai Li <cai.li@spreadtrum.com>,
        Orson Zhai <orson.zhai@spreadtrum.com>
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On 21 November 2017 at 03:12, Stephen Boyd <sboyd@codeaurora.org> wrote:
> On 11/20, Chunyan Zhang wrote:
>> From: Cai Li <cai.li@spreadtrum.com>
>>
>> In some cases the clock parent would be set NULL when doing re-parent,
>> it will cause a NULL pointer accessing if clk_set trace event is enabled,
>> since the trace event function would not check the input parameter.
>>
>> Signed-off-by: Cai Li <cai.li@spreadtrum.com>
>> Signed-off-by: Chunyan Zhang <chunyan.zhang@spreadtrum.com>
>
> Fixes: tag?
>
>> ---
>>  drivers/clk/clk.c | 9 ++++-----
>>  1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
>> index c8d83ac..64efaf0 100644
>> --- a/drivers/clk/clk.c
>> +++ b/drivers/clk/clk.c
>> @@ -1242,13 +1242,12 @@ static int __clk_set_parent(struct clk_core *core, struct clk_core *parent,
>>
>>       old_parent = __clk_set_parent_before(core, parent);
>>
>> -     trace_clk_set_parent(core, parent);
>> -
>>       /* change clock input source */
>> -     if (parent && core->ops->set_parent)
>> +     if (parent && core->ops->set_parent) {
>> +             trace_clk_set_parent(core, parent);
>>               ret = core->ops->set_parent(core->hw, p_index);
>> -
>> -     trace_clk_set_parent_complete(core, parent);
>> +             trace_clk_set_parent_complete(core, parent);
>> +     }
>
> Is the problem that parent may be NULL and the tracepoint
> dereferences it?

Yes, I think that probably is uncommon usage though, it revealed that
the tracepoint could be stronger :)

> Perhaps we need to update the tracepoint code
> instead so that we always see that the tracepoint is called even
> if we don't actually touch the hardware. Something like the patch
> below instead.

Ok, we will cook a new patch according to your comments.

Thanks,
Chunyan

>
> ---8<----
> diff --git a/include/trace/events/clk.h b/include/trace/events/clk.h
> index 758607226bfd..5a85ea2090c4 100644
> --- a/include/trace/events/clk.h
> +++ b/include/trace/events/clk.h
> @@ -139,7 +139,7 @@ DECLARE_EVENT_CLASS(clk_parent,
>
>         TP_fast_assign(
>                 __assign_str(name, core->name);
> -               __assign_str(pname, parent->name);
> +               __assign_str(pname, parent ? parent->name : NULL);
>         ),
>
>         TP_printk("%s %s", __get_str(name), __get_str(pname))
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
> a Linux Foundation Collaborative Project

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