Re: Crash in msm serial on dragonboard with ftrace bootargs

Sai Prakash Ranjan
2018-10-16T18:05:00Z

On 10/16/2018 11:18 PM, Steven Rostedt wrote:
> On Tue, 16 Oct 2018 23:06:24 +0530
> Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org> wrote:
>
>> On 10/16/2018 10:27 PM, Steven Rostedt wrote:
>>>
>>> OK, can you add to the command line:
>>>
>>> ftrace=function ftrace_filter=*schedule*
>>>
>>> to see if it's a specific function that may be causing the issue (but
>>> hopefully it's not one of the scheduling functions that caused it).
>>>
>>
>> Target boots fine with this. So its not scheduling functions that is
>> causing it. Also I tried with ftrace_filter=*msm* just to be sure if
>> tracing driver functions is causing any issue but its NOT.
>
> OK, seems that something is being traced that shouldn't be.
>
> When this happens after boot up, it's easy to bisect down to the
> problem function. But since it's at boot up, it will take a lot longer.
>
> I would suggest to start by going down the alphabet.
>
> ftrace_filter=a*
> ftrace_filter=b*
> ftrace_filter=c*
> [...]
>
> And at least find the letter the bad function starts with.
>
> Note, it could be more than one function (I've had that a couple of
> times), and to find that out, you can test with "ftrace_notrace". Say
> you find that the problem function starts with 'x'. You can do:
>
> ftrace_notrace=x*
>
> Which will trace all functions except those that start with an 'x', to
> make sure it still boots.
>
> Remember, you still need to have ftrace=function for all of this.
>
> Once you find the letter of the function, you can try the next letter,
> or perhaps come up with another method. I would say look at the
> functions in /sys/kernel/debug/tracing/available_filter_functions, but
> they don't list the init function (that can be traced). But you can
> use /proc/kallsyms instead.
>

Ok got it, this sounds fun. I'll give it a try.

Thanks

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