linux-kernel - Re: [PATCH 0/6] Tracing register accesses with pstore and dynamic debug

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Date:   Sat, 20 Oct 2018 09:27:19 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Laura Abbott <labbott@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Colin Cross <ccross@...roid.com>,
        Jason Baron <jbaron@...mai.com>,
        Tony Luck <tony.luck@...el.com>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Joe Perches <joe@...ches.com>,
        Jim Cromie <jim.cromie@...il.com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Prasad Sodagudi <psodagud@...eaurora.org>,
        tsoni@...eaurora.org, Bryan Huntsman <bryanh@...eaurora.org>,
        Tingwei Zhang <tingwei@...eaurora.org>, tkjos@...gle.com
Subject: Re: [PATCH 0/6] Tracing register accesses with pstore and dynamic
 debug

On Sat, Oct 20, 2018 at 12:02:37PM +0530, Sai Prakash Ranjan wrote:
> On 10/20/2018 10:55 AM, Joel Fernandes wrote:
> > On Sun, Sep 09, 2018 at 01:57:01AM +0530, Sai Prakash Ranjan wrote:
> > > Hi,
> > > 
> > > This patch series adds Event tracing support to pstore and is continuation
> > > to the RFC patch introduced to add a new tracing facility for register
> > > accesses called Register Trace Buffer(RTB). Since we decided to not introduce
> > > a separate framework to trace register accesses and use existing framework
> > > like tracepoints, I have moved from RFC. Details of the RFC in link below:
> > > 
> > > Link: https://lore.kernel.org/lkml/cover.1535119710.git.saiprakash.ranjan@codeaurora.org/
> > > 
> > > MSR tracing example given by Steven was helpful in using tracepoints for
> > > register accesses instead of using separate trace. But just having these
> > > IO traces would not help much unless we could have them in some persistent
> > > ram buffer for debugging unclocked access or some kind of bus hang or an
> > > unexpected reset caused by some buggy driver which happens a lot during
> > > initial development stages. By analyzing the last few entries of this buffer,
> > > we could identify the register access which is causing the issue.
> > 
> > Hi Sai,
> > 
> > I wanted to see if I could make some time to get your patches working. We are
> > hitting usecases that need something like this as well. Basically devices
> > hanging and then the ramdump does not tell us much, so in this case pstore
> > events can be really helpful. This usecase came up last year as well.
> > 
> > Anyway while I was going through your patches, I cleaned up some pstore code
> > as well and I have 3 more patches on top of yours for this clean up. I prefer
> > we submit the patches together and sync our work together so that there is
> > least conflict.
> > 
> > Here's my latest tree:
> > https://github.com/joelagnel/linux-kernel/commits/pstore-events
> > (note that I have only build tested the patches since I just wrote them and
> > its quite late in the night here ;-))
> > 
> 
> Hi Joel,
> 
> Thanks for looking into this. Sure, I will be happy to sync up with you on

Thanks. And added a fourth patch in the tree too.

> this. I can test your additional patches on top of my pstore patches. BTW,
> I'm still stuck at copying binary record into pstore and then extract it
> during read time. Seems like I'm missing something.

Sure, push your latest somewhere and let me know. I'll try to get you unstuck.

thanks,

 - Joel