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

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Message-ID: <20181019111205.5c8e98e8@gandalf.local.home>
Date:   Fri, 19 Oct 2018 11:12:05 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.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 Fri, 19 Oct 2018 20:18:19 +0530
Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org> wrote:


> > 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.

I'm saying there's a combination of the two. Because when ftrace is not
involved, early con doesn't crash.

I would focus on why earlycon crashes when only msm_read is traced.
That should help narrow down the cause.

What we know is:

	earlycon -> boots

	ftrace=function -> boots

 	earlycon ftrace=function ftrace_filter=msm_read -> crashes

If we remove the "ftrace=function ftrace_filter=msm_read" it boots
fine, and I'm assuming that if we just remove earlycon (keeping the
ftrace_filter), it also boots too.

Thus, ftrace tracing msm_read is causing earlycon to do something that
triggers the crash.

-- Steve