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

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Message-ID: <9cafe321-87f6-98a3-3bda-c2f7a3d7fc67@codeaurora.org>
Date:   Fri, 19 Oct 2018 20:18:19 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        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>,
        Kees Cook <keescook@...omium.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 10/19/2018 7:21 PM, Steven Rostedt wrote:
> On Fri, 19 Oct 2018 12:24:05 +0530
> Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org> wrote:
> 
>>>> Anyone see any problems here?
>>>
>>> This seems sane to me, he says in the other thread that he put 'notrace' to
>>> the msm serial functions (which AIUI should prevent ftrace instrumentation)
>>> and he still sees the issue.
>>>    
>>
>> Yes I did add notrace to all functions in msm serial and checked the
>> objdump to make sure that those were not instrumented, and yet the
>> target crashed. This doesnt seem like an issue with ftrace but rather
>> with msm early con.
> 
> The thing that still bothers me is that it boots fine without ftrace
> running, and that it requires tracing something to cause the problem.
> This tells me that ftrace has something to do with it. Perhaps it's
> just changing the timing.
> 

Yes tracing does cause issue but only if earlycon is present. If I 
disable earlycon, then even tracing wont cause any issue and target 
boots fine.

> You said that if you add 'ftrace_filter=msm_read' to the command line,
> it still crashes?
> 
> So only tracing that function we have an issue, right?
> 

Tracing msm_read does cause the crash, but that is not the only one 
causing the crash because even after "ftrace_notrace=msm_read" the board 
crashes which is why I suspect msm earlycon and not ftrace.

Thanks,
Sai
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