Re: Crash in msm serial on dragonboard with ftrace bootargs

From: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Stephen Boyd <sboyd@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Andy Gross <andy.gross@linaro.org>,
	David Brown <david.brown@linaro.org>,
	Jiri Slaby <jslaby@suse.com>,
	"Ivan T. Ivanov" <ivan.ivanov@linaro.org>,
	Kees Cook <keescook@chromium.org>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	Geliang Tang <geliangtang@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Pramod Gurav <gpramod@codeaurora.org>,
	linux-arm-msm@vger.kernel.org, linux-soc@vger.kernel.org,
	linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
	Rajendra Nayak <rnayak@codeaurora.org>,
	Vivek Gautam <vivek.gautam@codeaurora.org>,
	Sibi Sankar <sibis@codeaurora.org>
Subject: Re: Crash in msm serial on dragonboard with ftrace bootargs
Date: Tue, 16 Oct 2018 23:35:00 +0530	[thread overview]
Message-ID: <472db11e-49a6-a1ee-e298-791ee1bbb10b@codeaurora.org> (raw)
In-Reply-To: <20181016134803.1b9260c1@gandalf.local.home>

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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