Re: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17

[Jacob Pan]

On Fri, 18 Mar 2016 16:56:41 -0700
"Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote:

> On Fri, Mar 18, 2016 at 02:00:11PM -0700, Josh Triplett wrote:
> > On Thu, Feb 25, 2016 at 04:56:38PM -0800, Paul E. McKenney wrote:
> > > On Thu, Feb 25, 2016 at 04:13:11PM +1100, Ross Green wrote:
> > > > On Wed, Feb 24, 2016 at 8:28 AM, Ross Green
> > > > <rgkernel@xxxxxxxxx> wrote:
> > > > > On Wed, Feb 24, 2016 at 7:55 AM, Paul E. McKenney
> > > > > <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> > > 
> > > [ . . . ]
> > > 
> > > > >> Still working on getting decent traces...
> > > 
> > > And I might have succeeded, see below.
> > > 
> > > > >>
> > > > >>                                                         Thanx,
> > > > >> Paul
> > > > >>
> > > > >
> > > > > G'day all,
> > > > >
> > > > > Here is another dmesg output for 4.5-rc5 showing another
> > > > > rcu_preempt stall. This one appeared after only a day of
> > > > > running. CONFIG_DEBUG_TIMING is turned on, but can't see any
> > > > > output that shows from this.
> > > > >
> > > > > Again testing as before,
> > > > >
> > > > > Boot, run a series of small benchmarks, then just let the
> > > > > system be and idle away.
> > > > >
> > > > > I notice in the stack trace there is mention of
> > > > > hrtimer_run_queues and hrtimer_interrupt.
> > > > >
> > > > > Anyway, leave this for a few more eyes to look at.
> > > > >
> > > > > Open to any other suggestions of things to test.
> > > > >
> > > > > Regards,
> > > > >
> > > > > Ross Green
> > > > 
> > > > 
> > > > G'day Paul,
> > > > 
> > > > I left the pandaboard running and captured another stall.
> > > > 
> > > > the attachment is the dmesg output.
> > > > 
> > > > Again there is no apparent output from any CONFIG_DEBUG_TIMING
> > > > so I assume there is nothing happening there.
> > > 
> > > I agree, looks like this is not due to time skew.
> > > 
> > > > I just saw the updates for 4.6 RCU code.
> > > > Is the patch in [PATCH tip/core/rcu 04/13] valid here?
> > > 
> > > I doubt that it will help, but you never know.
> > > 
> > > > do you want me try the new patch set with this configuration?
> > > 
> > > Even better would be to try Daniel Wagner's swait patchset.  I
> > > have attached them in UNIX mbox format, or you can get them from
> > > the -tip tree.
> > > 
> > > And I -finally- got some tracing that -might- be useful.  The
> > > dmesg, all 67MB of it, is here:
> > > 
> > > 	http://www.rdrop.com/~paulmck/submission/console.2016.02.23a.log
> > > 
> > > This failure mode is less likely to happen, and looks a bit
> > > different than the ones that I was seeing before enabling
> > > tracing.  Then, an additional wakeup would actually wake the task
> > > up.  In contrast, with tracing enabled, the RCU grace-period
> > > kthread goes into "teenager mode", refusing to wake up despite
> > > repeated attempts.  However, this might be a side-effect of the
> > > ftrace dump.
> > > 
> > > On line 525,132, we see that the rcu_preempt grace-period kthread
> > > has been starved for 1,188,154 jiffies, or about 20 minutes.
> > > This seems unlikely...  The kthread is waiting for no more than a
> > > three-jiffy timeout ("RCU_GP_WAIT_FQS(3)") and is in
> > > TASK_INTERRUPTIBLE state ("0x1").
> > 
> > We're seeing a similar stall (~60 seconds) on an x86 development
> > system here.  Any luck tracking down the cause of this?  If not, any
> > suggestions for traces that might be helpful?
> 
> The dmesg containing the stall, the kernel version, and the .config
> would be helpful!  Working on a torture test specific to this bug...
> 
> 							Thanx, Paul
> 
+Reinette, she has the system that can reproduce the issue. I
believe she is having some other problems with it at the moment. But
the .config should be available. Version is v4.5.