Re: Query: rcu_sched detected stalls with function_graph tracer

[Steven Rostedt]

On Wed, 2 Aug 2017 12:02:21 +0530
Pratyush Anand <panand@xxxxxxxxxx> 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