Re: [BUG] ftrace: WARNING: suspicious RCU usage

[Masami Hiramatsu]

On Tue, 27 Jun 2017 09:29:26 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Tue, 27 Jun 2017 20:51:26 +0900
> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
> 
> > Hello Steve,
> > 
> > I've faced the following RCU warning while I ran ftracetest testcase
> > "ftrace - function graph filters with stack tracer" on qemu.
> > The kernel is ftrace/core branch.
> > 
> > [   10.919174] =============================
> > [   10.920077] WARNING: suspicious RCU usage
> > [   10.920977] 4.12.0-rc5+ #1 Not tainted
> > [   10.921828] -----------------------------
> > [   10.922748] /home/mhiramat/ksrc/linux/include/trace/events/rcu.h:454 suspicious rcu_dereference_check() usage!
> > [   10.924761] 
> > [   10.924761] other info that might help us debug this:
> > [   10.924761] 
> > [   10.926775] 
> > [   10.926775] RCU used illegally from idle CPU!
> > [   10.926775] rcu_scheduler_active = 2, debug_locks = 1
> > [   10.929176] RCU used illegally from extended quiescent state!
> > [   10.930525] no locks held by swapper/7/0.
> > [   10.931547] 
> > [   10.931547] stack backtrace:
> > [   10.932777] CPU: 7 PID: 0 Comm: swapper/7 Not tainted 4.12.0-rc5+ #1
> > [   10.934025] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.fc25 04/01/2014
> > [   10.935869] Call Trace:
> > [   10.936550]  dump_stack+0x86/0xcf
> > [   10.937359]  lockdep_rcu_suspicious+0xc5/0x100
> > [   10.938327]  ? rcu_eqs_exit_common.isra.53+0x5/0x150
> 
> > [   10.939229]  rcu_irq_enter+0x18d/0x1a0
> 
> Strange, it triggered in rcu_irq_enter()?
> 
> > [   10.939902]  ? rcu_eqs_exit_common.isra.53+0x5/0x150
> > [   10.940683]  check_stack+0xbb/0x2f0
> > [   10.941333]  stack_trace_call+0x3f/0x50
> > [   10.942010]  0xffffffffa0000077
> > [   10.942620]  ? ftrace_graph_caller+0x78/0xa8
> > [   10.943342]  ? rcu_eqs_exit_common.isra.53+0x5/0x150
> > [   10.944214]  ? rcu_idle_exit+0x5/0x90
> 
> > [   10.944937]  rcu_eqs_exit_common.isra.53+0x5/0x150
> 
> Hmm, we are tracing rcu_eqs_exit_common.
> 
> 
> Do you have this commit in this branch?
> 
> Commit 03ecd3f4 "rcu/tracing: Add rcu_disabled to denote when
> rcu_irq_enter() will not work"

Yes, that is merged.

Hmm, I'll check this is correctly enabled again, since this time
I couldn't reproduce it.

Thank you,

> 
> -- Steve
> 
> > [   10.945754]  rcu_idle_exit+0x8c/0x90
> > [   10.946612]  ? rcu_eqs_exit_common.isra.53+0x5/0x150
> > [   10.947414]  ? rcu_idle_exit+0x8c/0x90
> > [   10.948091]  do_idle+0x116/0x1c0
> > [   10.948797]  cpu_startup_entry+0x1d/0x20
> > [   10.949569]  start_secondary+0xfa/0x100
> > [   10.950335]  secondary_startup_64+0x9f/0x9f
> > [   10.951182] 
> > 
> > I attached full log and kconfig. I can reproduce it with just running
> > following script.
> > 
> > ----
> > cd tools/testing/selftests/ftrace
> > while true; do
> >         ./ftracetest test.d/ftrace/fgraph-filter-stack.tc
> > done
> > ----
> > 
> > Thank you,
> > 
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>