linux-kernel - Re: [PATCH 2/6] pstore: Add event tracing support

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Date:   Tue, 18 Sep 2018 16:44:34 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     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>,
        Joel Fernandes <joel@...lfernandes.org>,
        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>
Subject: Re: [PATCH 2/6] pstore: Add event tracing support

On Tue, 18 Sep 2018 23:22:48 +0530
Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org> wrote:

> On 9/18/2018 5:04 AM, Steven Rostedt wrote:
> > 
> > It looks like pstore_event_call() gets called from a trace event. You
> > can't call kmalloc() from one. One thing is that kmalloc has
> > tracepoints itself. You trace those you just entered an infinite loop.
> > 
> >   
> 
> Ok will remove it in v2. But any alternative way to do this?

I think I describe it below.

> 
> >> +
> >> +	event_call = fbuffer->trace_file->event_call;
> >> +	if (!event_call || !event_call->event.funcs ||
> >> +	    !event_call->event.funcs->trace)
> >> +		goto fail_event;
> >> +
> >> +	event = &fbuffer->trace_file->event_call->event;
> >> +
> >> +	spin_lock_irqsave(&psinfo->buf_lock, flags);
> >> +
> >> +	trace_seq_init(&iter->seq);
> >> +	iter->ent = fbuffer->entry;  
> > 
> > I guess what you are doing is needing to translate the raw data into
> > ascii output, and need the trace_iterator to do so.
> > 
> > You are already under a psinfo->buf_lock. Add a dummy iterator to that
> > and use it instead.
> > 
> > 	trace_seq_init(&psinfo->iter->seq);
> >   
> >> +	event_call->event.funcs->trace(iter, 0, event);  
> > 
> > 				      (psinfo->iter, 0 , event);
> > 
> > etc.
> >   
> 
> Sure, will update in v2.
> 
> >> +	trace_seq_putc(&iter->seq, 0);
> >> +
> >> +	if (seq->size > psinfo->bufsize)
> >> +		seq->size = psinfo->bufsize;
> >> +
> >> +	s = &iter->seq;
> >> +	seq = &s->seq;
> >> +
> >> +	record.buf = (char *)(seq->buffer);
> >> +	record.size = seq->len;
> >> +	psinfo->write(&record);
> >> +
> >> +	spin_unlock_irqrestore(&psinfo->buf_lock, flags);  
> > 
> > You may also need to convert these spin_locks into raw_spin_locks as
> > when PREEMPT_RT enters the kernel you don't want them to turn into
> > mutexes.
> > 
> > But that can be another patch.
> >   
> 
> I will change this in v2, but can't we have it in same patch?

I suggested a separate patch because buf_lock is used elsewhere.
Changing it to "raw_spin_lock" will affect more than just what this
patch series does. Thus, I recommend making it a separate patch to keep
this patch series from being more intrusive than it needs to be.

Thanks!

-- Steve