From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yanko Kaneti Subject: Re: localed stuck in recent 3.18 git in copy_net_ns? Date: Sat, 25 Oct 2014 00:25:57 +0300 Message-ID: <20141024212557.GA15537@declera.com> References: <1414100740.2065.2.camel@declera.com> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Josh Boyer , "Eric W. Biederman" , Cong Wang , Kevin Fenzi , netdev , "Linux-Kernel@Vger. Kernel. Org" , jay.vosburgh@canonical.com, mroos@linux.ee To: "Paul E. McKenney" Return-path: Content-Disposition: inline In-Reply-To: <20141024183226.GW4977@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri-10/24/14-2014 11:32, 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. Sorry for being unresposive here, but I know next to nothing about tracing or most things about the kernel, so I have some cathing up to do. In the meantime some layman observations while I tried to find what exactly triggers the problem. - Even in runlevel 1 I can reliably trigger the problem by starting libvirtd - libvirtd seems to be very active in using all sorts of kernel facilities that are modules on fedora so it seems to cause many simultaneous kworker calls to modprobe - there are 8 kworker/u16 from 0 to 7 - one of these kworkers always deadlocks, while there appear to be two kworker/u16:6 - the seventh 6 vs 8 as in 6 rcuos where before they were always 8 Just observations from someone who still doesn't know what the u16 kworkers are.. -- Yanko > 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; > > > } > > > > > >