On Thu, Oct 23, 2014 at 05:27:50AM -0700, Paul E. McKenney wrote:
> On Thu, Oct 23, 2014 at 09:09:26AM +0300, Yanko Kaneti wrote:
> > On Wed, 2014-10-22 at 16:24 -0700, Paul E. McKenney wrote:
> > > On Thu, Oct 23, 2014 at 01:40:32AM +0300, Yanko Kaneti wrote:
> > > > On Wed-10/22/14-2014 15:33, Josh Boyer wrote:
> > > > > On Wed, Oct 22, 2014 at 2:55 PM, Paul E. McKenney
> > > > > <paul...@linux.vnet.ibm.com> wrote:
> > >
> > > [ . . . ]
> > >
> > > > > > Don't get me wrong -- the fact that this kthread appears to
> > > > > > have
> > > > > > blocked within rcu_barrier() for 120 seconds means that
> > > > > > something is
> > > > > > most definitely wrong here. I am surprised that there are no
> > > > > > RCU CPU
> > > > > > stall warnings, but perhaps the blockage is in the callback
> > > > > > execution
> > > > > > rather than grace-period completion. Or something is
> > > > > > preventing this
> > > > > > kthread from starting up after the wake-up callback executes.
> > > > > > Or...
> > > > > >
> > > > > > Is this thing reproducible?
> > > > >
> > > > > I've added Yanko on CC, who reported the backtrace above and can
> > > > > recreate it reliably. Apparently reverting the RCU merge commit
> > > > > (d6dd50e) and rebuilding the latest after that does not show the
> > > > > issue. I'll let Yanko explain more and answer any questions you
> > > > > have.
> > > >
> > > > - It is reproducible
> > > > - I've done another build here to double check and its definitely
> > > > the rcu merge
> > > > that's causing it.
> > > >
> > > > Don't think I'll be able to dig deeper, but I can do testing if
> > > > needed.
> > >
> > > Please! Does the following patch help?
> >
> > Nope, doesn't seem to make a difference to the modprobe ppp_generic
> > test
>
> Well, I was hoping. I will take a closer look at the RCU merge commit
> and see what suggests itself. I am likely to ask you to revert specific
> commits, if that works for you.
Well, rather than reverting commits, could you please try testing the
following commits?
11ed7f934cb8 (rcu: Make nocb leader kthreads process pending callbacks after
spawning)
73a860cd58a1 (rcu: Replace flush_signals() with WARN_ON(signal_pending()))
c847f14217d5 (rcu: Avoid misordering in nocb_leader_wait())
For whatever it is worth, I am guessing this one.
a53dd6a65668 (rcutorture: Add RCU-tasks tests to default rcutorture list)
If any of the above fail, this one should also fail.
Also, could you please send along your .config?
Thanx, Paul
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