linux-kernel - Re: [BUG] function_graph trace causes hang when using sleepgraph (4.15.0-rc1 and newer)

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Message-ID: <1515467251.17761.14.camel@linux.intel.com>
Date:   Mon, 08 Jan 2018 19:07:31 -0800
From:   Todd Brandt <todd.e.brandt@...ux.intel.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        len.brown@...el.com, todd.e.brandt@...el.com
Subject: Re: [BUG] function_graph trace causes  hang when using sleepgraph
 (4.15.0-rc1 and newer)

On Mon, 2018-01-08 at 17:25 -0800, Todd Brandt wrote:
> On Mon, 2018-01-08 at 20:07 -0500, Steven Rostedt wrote:
> > On Mon, 08 Jan 2018 17:02:29 -0800
> > Todd Brandt <todd.e.brandt@...ux.intel.com> wrote:
> > 
> > > Stephen, the problem is reversed by removing the following two
> > > commits,
> > > the one the bisect showed and the very next. So the problem is
> > > here:
> > > 
> > > commit 1a149d7d3f45d311da1f63473736c05f30ae8a75
> > > Author: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > > Date:   Fri Sep 22 16:59:02 2017 -0400
> > > 
> > >     ring-buffer: Rewrite trace_recursive_(un)lock() to be simpler
> > 
> > This one still doesn't make sense, for why it would cause the hang.
> > 
> > 
> > > commit 12ecef0cb12102d8c034770173d2d1363cb97d52
> > > Author: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > > Date:   Thu Sep 21 16:22:49 2017 -0400
> > > 
> > >     tracing: Reverse the order of trace_types_lock and
> > > event_mutex
> > 
> > This one does.
> > 
> > Can you run lockdep when you do this and see if lockdep catches
> > anything? If it does, it should point directly to where the
> > inversed
> > locking happened.
> 
> Can you reproduce the issue there? I just want to be sure it's not
> something local to our machines here, as long as you have CONFIG_PM
> enabled it should work the same hopefully. 
> 
> I'll give lockdep a try here.

I tried lockdep here (/proc/lockdep*) but I can't get any useful data
after the hang beyond the last printk. Is there a way I can enclose the
device_pm_callback function in some kind of debug harness to prevent
the hang (sorry, I'm not terribly familiar with lockdep for kernel
level hangs)?


> 
> > 
> > -- Steve