linux-kernel - Re: Query: rcu_sched detected stalls with function

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Message-ID: <20170802075650.7dab7586@gandalf.local.home>
Date:   Wed, 2 Aug 2017 07:56:50 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Pratyush Anand <panand@...hat.com>
Cc:     open list <linux-kernel@...r.kernel.org>
Subject: Re: Query: rcu_sched detected stalls with function_graph tracer

On Wed, 2 Aug 2017 12:02:21 +0530
Pratyush Anand <panand@...hat.com> wrote:

> Hi Steve,
> 
> I am using a 3.10 based kernel, and when I enable function_graph with one 
> particular x86_64 machine, I encounter rcu_sched stall.
> 
> echo function_graph > /sys/kernel/debug/tracing/current_tracer
> echo 1 > /sys/kernel/debug/tracing/tracing_on
> 
> If I use 4.13-rc2, then its better, but still goes for it after a bit of 
> stressing with stressng.
> 
> It looks like that this behavior should be expected with a loaded system (like 
> that of ftrace-graph tracing for all available function) which can cause RCU 
> stall warning. But,I am not an expert. So, whats your opinion on it?
> 
> I tried to bisect and there was no particular function which can cause this. 
> It looked like that when we had more than 5000 functions in set_ftrace_filter, 
> we start getting such warnings. Tried by putting some most  hit functions like 
> spin_lock* etc in set_ftrace_notrace. Still, no help.  Do you have some 
> suggestion for further debugging pointers?
> 
> log with 3.10 based kernel

Can you send me the config. I'm also guessing that this is a RHEL 3.10
based kernel (which means it's not 3.10 at all).

-- Steve