Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755461AbaJXWCW (ORCPT ); Fri, 24 Oct 2014 18:02:22 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35841 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751573AbaJXWCU (ORCPT ); Fri, 24 Oct 2014 18:02:20 -0400 From: Jay Vosburgh To: paulmck@linux.vnet.ibm.com cc: Yanko Kaneti , Josh Boyer , "Eric W. Biederman" , Cong Wang , Kevin Fenzi , netdev , "Linux-Kernel@Vger. Kernel. Org" , mroos@linux.ee, tj@kernel.org Subject: Re: localed stuck in recent 3.18 git in copy_net_ns? In-reply-to: <20141024214927.GA4977@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> <20141024212557.GA15537@declera.com> <20141024214927.GA4977@linux.vnet.ibm.com> Comments: In-reply-to "Paul E. McKenney" message dated "Fri, 24 Oct 2014 14:49:27 -0700." X-Mailer: MH-E 8.5+bzr; nmh 1.5; GNU Emacs 24.4.50 Date: Fri, 24 Oct 2014 15:02:04 -0700 Message-ID: <8451.1414188124@famine> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paul E. McKenney wrote: >On Sat, Oct 25, 2014 at 12:25:57AM +0300, Yanko Kaneti wrote: >> 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: > >[ . . . ] > >> > > > 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 > >Adding Tejun on CC in case this duplication of kworker/u16:6 is important. > >> 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.. > >Could you please run the following diagnostic patch? This will help >me see if I have managed to miswire the rcuo kthreads. It should >print some information at task-hang time. I can give this a spin after the ftrace (now that I've got CONFIG_RCU_TRACE turned on). I've got an ftrace capture from unmodified -net, it looks like this: ovs-vswitchd-902 [000] .... 471.778441: rcu_barrier: rcu_sched Begin cpu -1 remaining 0 # 0 ovs-vswitchd-902 [000] .... 471.778452: rcu_barrier: rcu_sched Check cpu -1 remaining 0 # 0 ovs-vswitchd-902 [000] .... 471.778452: rcu_barrier: rcu_sched Inc1 cpu -1 remaining 0 # 1 ovs-vswitchd-902 [000] .... 471.778453: rcu_barrier: rcu_sched OnlineNoCB cpu 0 remaining 1 # 1 ovs-vswitchd-902 [000] .... 471.778453: rcu_barrier: rcu_sched OnlineNoCB cpu 1 remaining 2 # 1 ovs-vswitchd-902 [000] .... 471.778453: rcu_barrier: rcu_sched OnlineNoCB cpu 2 remaining 3 # 1 ovs-vswitchd-902 [000] .... 471.778454: rcu_barrier: rcu_sched OnlineNoCB cpu 3 remaining 4 # 1 ovs-vswitchd-902 [000] .... 471.778454: rcu_barrier: rcu_sched Inc2 cpu -1 remaining 4 # 2 rcuos/0-9 [000] ..s. 471.793150: rcu_barrier: rcu_sched CB cpu -1 remaining 3 # 2 rcuos/1-18 [001] ..s. 471.793308: rcu_barrier: rcu_sched CB cpu -1 remaining 2 # 2 I let it sit through several "hung task" cycles but that was all there was for rcu:rcu_barrier. I should have ftrace with the patch as soon as the kernel is done building, then I can try the below patch (I'll start it building now). -J > Thanx, Paul > >------------------------------------------------------------------------ > >rcu: Dump no-CBs CPU state at task-hung time > >Strictly diagnostic commit for rcu_barrier() hang. Not for inclusion. > >Signed-off-by: Paul E. McKenney > >diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h >index 0e5366200154..34048140577b 100644 >--- a/include/linux/rcutiny.h >+++ b/include/linux/rcutiny.h >@@ -157,4 +157,8 @@ static inline bool rcu_is_watching(void) > > #endif /* #else defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ > >+static inline void rcu_show_nocb_setup(void) >+{ >+} >+ > #endif /* __LINUX_RCUTINY_H */ >diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h >index 52953790dcca..0b813bdb971b 100644 >--- a/include/linux/rcutree.h >+++ b/include/linux/rcutree.h >@@ -97,4 +97,6 @@ extern int rcu_scheduler_active __read_mostly; > > bool rcu_is_watching(void); > >+void rcu_show_nocb_setup(void); >+ > #endif /* __LINUX_RCUTREE_H */ >diff --git a/kernel/hung_task.c b/kernel/hung_task.c >index 06db12434d72..e6e4d0f6b063 100644 >--- a/kernel/hung_task.c >+++ b/kernel/hung_task.c >@@ -118,6 +118,7 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) > " disables this message.\n"); > sched_show_task(t); > debug_show_held_locks(t); >+ rcu_show_nocb_setup(); > > touch_nmi_watchdog(); > >diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c >index 240fa9094f83..6b373e79ce0e 100644 >--- a/kernel/rcu/rcutorture.c >+++ b/kernel/rcu/rcutorture.c >@@ -1513,6 +1513,7 @@ rcu_torture_cleanup(void) > { > int i; > >+ rcu_show_nocb_setup(); > rcutorture_record_test_transition(); > if (torture_cleanup_begin()) { > if (cur_ops->cb_barrier != NULL) >diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h >index 927c17b081c7..285b3f6fb229 100644 >--- a/kernel/rcu/tree_plugin.h >+++ b/kernel/rcu/tree_plugin.h >@@ -2699,6 +2699,31 @@ static bool init_nocb_callback_list(struct rcu_data *rdp) > > #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ > >+void rcu_show_nocb_setup(void) >+{ >+#ifdef CONFIG_RCU_NOCB_CPU >+ int cpu; >+ struct rcu_data *rdp; >+ struct rcu_state *rsp; >+ >+ for_each_rcu_flavor(rsp) { >+ pr_alert("rcu_show_nocb_setup(): %s nocb state:\n", rsp->name); >+ for_each_possible_cpu(cpu) { >+ if (!rcu_is_nocb_cpu(cpu)) >+ continue; >+ rdp = per_cpu_ptr(rsp->rda, cpu); >+ pr_alert("%3d: %p l:%p n:%p %c%c%c\n", >+ cpu, >+ rdp, rdp->nocb_leader, rdp->nocb_next_follower, >+ ".N"[!!rdp->nocb_head], >+ ".G"[!!rdp->nocb_gp_head], >+ ".F"[!!rdp->nocb_follower_head]); >+ } >+ } >+#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ >+} >+EXPORT_SYMBOL_GPL(rcu_show_nocb_setup); >+ > /* > * An adaptive-ticks CPU can potentially execute in kernel mode for an > * arbitrarily long period of time with the scheduling-clock tick turned > --- -Jay Vosburgh, jay.vosburgh@canonical.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/