Messages in this thread | | | Subject | Re: linux-next 20111025: warnings in rcu_idle_exit_common()/rcu_idle_enter_common() | From | Steven Rostedt <> | Date | Mon, 31 Oct 2011 11:44:42 -0400 |
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On Mon, 2011-10-31 at 05:19 -0700, Paul E. McKenney wrote: > On Mon, Oct 31, 2011 at 07:41:42PM +0800, Wu Fengguang wrote: > > On Mon, Oct 31, 2011 at 06:43:25PM +0800, Wu Fengguang wrote: > > > On Mon, Oct 31, 2011 at 05:51:52PM +0800, Paul E. McKenney wrote: > > > > On Mon, Oct 31, 2011 at 04:26:34PM +0800, Wu Fengguang wrote: > > > > > Hi Paul, > > > > > > > > > > I got two warnings in rcutree.c. The last working kernels are > > > > > linux-next 20111014 and linux v3.1. > > > > > > > > Interesting. Could you please enable RCU event tracing at boot? > > > > > > Sorry I cannot...possibly due to another ftrace bug. > > > > > > > The RCU event tracing is at tracing/events/rcu/enable relative to > > > > the debugfs mount point at runtime, if that helps. > > > > > > It's exactly that linux next 20111025 (comparing to 20111014) no > > > longer produces all the trace events that made me looking into the > > > dmesg and find the warning from RCU (rather than the expected warning > > > from ftrace). > > > > > > The trace output is now: > > > > > > # tracer: nop > > > # > > > # WARNING: FUNCTION TRACING IS CORRUPTED > > > # MAY BE MISSING FUNCTION EVENTS > > > # TASK-PID CPU# TIMESTAMP FUNCTION > > > # | | | | | > > > (nothing more) > > > > I checked the other test box and got the same warnings. Below is the > > full dmesg. > > > > No single trace output again.. > > Hmmm... I wonder if it is too early during boot for tracing to work > correctly. > > Gah! I have rcu/next set ahead to commits that are not supposed to go > upstream yet. I reset it back to match the stuff that is targeted for > the current merge window. Still need to find the bug, of course. > > Anyone have any idea why the kworker thread might be trying to enter > the idle loop? The idle_cpu(smp_processor_id()) call believes that > this is not the idle task. Or does x86 allow non-idle tasks to enter > the idle loop? Or to be migrated off-CPU?
It's not. Carsten Emde noticed what looked like a bug in ftrace last week at LinuxCon, and looking deeper at it, I found that the swapper task for all but CPU0 is named kworker. That's because kworker creates the idle task for all other CPUs besides CPU 0 and the idle task takes on kworker name.
Carsten posted a patch last week too:
https://lkml.org/lkml/2011/10/26/313
I'm glad that this bug shows up outside of just ftrace :)
-- Steve
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