linux-kernel - Re: Crash in msm serial on dragonboard with ftrace bootargs

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Date:   Tue, 16 Oct 2018 23:35:00 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Jiri Slaby <jslaby@...e.com>,
        "Ivan T. Ivanov" <ivan.ivanov@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Geliang Tang <geliangtang@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pramod Gurav <gpramod@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>
Subject: Re: Crash in msm serial on dragonboard with ftrace bootargs

On 10/16/2018 11:18 PM, Steven Rostedt wrote:
> On Tue, 16 Oct 2018 23:06:24 +0530
> Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.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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