From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: localed stuck in recent 3.18 git in copy_net_ns? Date: Fri, 24 Oct 2014 11:57:53 -0700 Message-ID: <20141024185753.GY4977@linux.vnet.ibm.com> References: <20141023220406.GJ4977@linux.vnet.ibm.com> <20141024090857.GA4083@declera.com> <20141024154006.GP4977@linux.vnet.ibm.com> <20141024162943.GA16621@declera.com> <20141024165454.GS4977@linux.vnet.ibm.com> <20141024170931.GA21849@declera.com> <20141024172009.GV4977@linux.vnet.ibm.com> <20141024173526.GA26058@declera.com> <20141024183226.GW4977@linux.vnet.ibm.com> <6050.1414176588@famine> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Yanko Kaneti , Josh Boyer , "Eric W. Biederman" , Cong Wang , Kevin Fenzi , netdev , "Linux-Kernel@Vger. Kernel. Org" , mroos@linux.ee To: Jay Vosburgh Return-path: Content-Disposition: inline In-Reply-To: <6050.1414176588@famine> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Oct 24, 2014 at 11:49:48AM -0700, Jay Vosburgh wrote: > Paul E. McKenney 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. 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.vosburgh@canonical.com >