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

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Date:   Wed, 10 Jan 2018 16:21:08 -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 Tue, 2018-01-09 at 11:13 -0500, Steven Rostedt wrote:
> On Mon, 08 Jan 2018 17:25:15 -0800
> Todd Brandt <todd.e.brandt@...ux.intel.com> wrote:
> 
> > 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. 
> 
> Just to let you know, I'm currently traveling, so my testing ability
> is
> limited at the time being.

ok, it's not an emergency, we're using a patched version of the kernel
with those two commits removed in the interim. I tried running kgdb
over serial console, but unfortunately it doesn't work over a USB-to-
Serial dongle (even Greg K-H says it won't work, :P). This is the best
output I could get, considering:

# run the test script here
[  545.733458] PM: suspend entry (deep)
[  545.734535] PM: Syncing filesystems ... done.
[  546.580551] Freezing user space processes ... (elapsed 0.013
seconds) done.
[  546.594846] OOM killer disabled.
[  546.595002] Freezing remaining freezable tasks ... (elapsed 0.005
seconds) done.
[  557.808719] NMI watchdog: Watchdog detected hard LOCKUP on cpu 0

So it's definitely a hard lockup, I just can't get the stack trace
without a system with a built in serial console.

> 
> -- Steve