On Fri, Oct 24, 2014 at 11:57:53AM -0700, Paul E. McKenney wrote:
> On Fri, Oct 24, 2014 at 11:49:48AM -0700, Jay Vosburgh wrote:
> > Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote:
> >
> > >On Fri, Oct 24, 2014 at 08:35:26PM +0300, Yanko Kaneti wrote:
> > >> On Fri-10/24/14-2014 10:20, Paul E. McKenney wrote:
> > >> > On Fri, Oct 24, 2014 at 08:09:31PM +0300, Yanko Kaneti wrote:
> > >> > > On Fri-10/24/14-2014 09:54, Paul E. McKenney wrote:
> > >> > > > On Fri, Oct 24, 2014 at 07:29:43PM +0300, Yanko Kaneti wrote:
> > >> > > > > On Fri-10/24/14-2014 08:40, Paul E. McKenney wrote:
> > >> > > > > > On Fri, Oct 24, 2014 at 12:08:57PM +0300, Yanko Kaneti wrote:
> > >> > > > > > > On Thu-10/23/14-2014 15:04, Paul E. McKenney wrote:
> > >> > > > > > > > On Fri, Oct 24, 2014 at 12:45:40AM +0300, Yanko Kaneti
> > >> > > > > > > > wrote:
> > >> > > > > > > > >
> > >> > > > > > > > > On Thu, 2014-10-23 at 13:05 -0700, Paul E. McKenney
> > >> > > > > > > > > wrote:
> > >> > > > > > > > > > On Thu, Oct 23, 2014 at 10:51:59PM +0300, Yanko Kaneti
> > >> > > > > > > > > > wrote:
> > >> > > >
> > >> > > > [ . . . ]
> > >> > > >
> > >> > > > > > > Ok, unless I've messsed up something major, bisecting points
> > >> > > > > > > to:
> > >> > > > > > >
> > >> > > > > > > 35ce7f29a44a rcu: Create rcuo kthreads only for onlined CPUs
> > >> > > > > > >
> > >> > > > > > > Makes any sense ?
> > >> > > > > >
> > >> > > > > > Good question. ;-)
> > >> > > > > >
> > >> > > > > > Are any of your online CPUs missing rcuo kthreads? There
> > >> > > > > > should be
> > >> > > > > > kthreads named rcuos/0, rcuos/1, rcuos/2, and so on for each
> > >> > > > > > online CPU.
> > >> > > > >
> > >> > > > > Its a Phenom II X6. With 3.17 and linux-tip with 35ce7f29a44a
> > >> > > > > reverted, the rcuos are 8
> > >> > > > > and the modprobe ppp_generic testcase reliably works, libvirt
> > >> > > > > also manages
> > >> > > > > to setup its bridge.
> > >> > > > >
> > >> > > > > Just with linux-tip , the rcuos are 6 but the failure is as
> > >> > > > > reliable as
> > >> > > > > before.
> > >> > >
> > >> > > > Thank you, very interesting. Which 6 of the rcuos are present?
> > >> > >
> > >> > > Well, the rcuos are 0 to 5. Which sounds right for a 6 core CPU like
> > >> > > this
> > >> > > Phenom II.
> > >> >
> > >> > Ah, you get 8 without the patch because it creates them for potential
> > >> > CPUs as well as real ones. OK, got it.
> > >> >
> > >> > > > > Awating instructions: :)
> > >> > > >
> > >> > > > Well, I thought I understood the problem until you found that only
> > >> > > > 6 of
> > >> > > > the expected 8 rcuos are present with linux-tip without the
> > >> > > > revert. ;-)
> > >> > > >
> > >> > > > I am putting together a patch for the part of the problem that I
> > >> > > > think
> > >> > > > I understand, of course, but it would help a lot to know which two
> > >> > > > of
> > >> > > > the rcuos are missing. ;-)
> > >> > >
> > >> > > Ready to test
> > >> >
> > >> > Well, if you are feeling aggressive, give the following patch a spin.
> > >> > I am doing sanity tests on it in the meantime.
> > >>
> > >> Doesn't seem to make a difference here
> > >
> > >OK, inspection isn't cutting it, so time for tracing. Does the system
> > >respond to user input? If so, please enable rcu:rcu_barrier ftrace before
> > >the problem occurs, then dump the trace buffer after the problem occurs.
> >
> > My system is up and responsive when the problem occurs, so this
> > shouldn't be a problem.
>
> Nice! ;-)
>
> > Do you want the ftrace with your patch below, or unmodified tip
> > of tree?
>
> Let's please start with the patch.
And I should hasten to add that you need to set CONFIG_RCU_TRACE=y
for these tracepoints to be enabled.
Thanx, Paul
> > -J
> >
> >
> > > Thanx, Paul
> > >
> > >> > ------------------------------------------------------------------------
> > >> >
> > >> > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> > >> > index 29fb23f33c18..927c17b081c7 100644
> > >> > --- a/kernel/rcu/tree_plugin.h
> > >> > +++ b/kernel/rcu/tree_plugin.h
> > >> > @@ -2546,9 +2546,13 @@ static void rcu_spawn_one_nocb_kthread(struct
> > >> > rcu_state *rsp, int cpu)
> > >> > rdp->nocb_leader = rdp_spawn;
> > >> > if (rdp_last && rdp != rdp_spawn)
> > >> > rdp_last->nocb_next_follower = rdp;
> > >> > - rdp_last = rdp;
> > >> > - rdp = rdp->nocb_next_follower;
> > >> > - rdp_last->nocb_next_follower = NULL;
> > >> > + if (rdp == rdp_spawn) {
> > >> > + rdp = rdp->nocb_next_follower;
> > >> > + } else {
> > >> > + rdp_last = rdp;
> > >> > + rdp = rdp->nocb_next_follower;
> > >> > + rdp_last->nocb_next_follower = NULL;
> > >> > + }
> > >> > } while (rdp);
> > >> > rdp_spawn->nocb_next_follower = rdp_old_leader;
> > >> > }
> > >> >
> >
> > ---
> > -Jay Vosburgh, jay.vosbu...@canonical.com
> >
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