Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751995AbaJWGQL (ORCPT ); Thu, 23 Oct 2014 02:16:11 -0400 Received: from mail.declera.com ([87.118.141.5]:56791 "HELO mail.declera.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750827AbaJWGQJ (ORCPT ); Thu, 23 Oct 2014 02:16:09 -0400 X-Greylist: delayed 400 seconds by postgrey-1.27 at vger.kernel.org; Thu, 23 Oct 2014 02:16:08 EDT Message-ID: <1414044566.2031.1.camel@declera.com> Subject: Re: localed stuck in recent 3.18 git in copy_net_ns? From: Yanko Kaneti To: paulmck@linux.vnet.ibm.com Cc: Josh Boyer , "Eric W. Biederman" , Cong Wang , Kevin Fenzi , netdev , "Linux-Kernel@Vger. Kernel. Org" Date: Thu, 23 Oct 2014 09:09:26 +0300 In-Reply-To: <20141022232421.GN4977@linux.vnet.ibm.com> References: <20141020145359.565fe5e6@voldemort.scrye.com> <20141021151225.5df96645@voldemort.scrye.com> <8738aghtyj.fsf@x220.int.ebiederm.org> <20141022181135.GH4977@linux.vnet.ibm.com> <87d29kezby.fsf@x220.int.ebiederm.org> <20141022185511.GI4977@linux.vnet.ibm.com> <20141022224032.GA1240@declera.com> <20141022232421.GN4977@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.13.6 (3.13.6-1.fc22) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > > 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 INFO: task kworker/u16:6:101 blocked for more than 120 seconds. Not tainted 3.18.0-0.rc1.git2.3.fc22.x86_64 #1 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. kworker/u16:6 D ffff88022067cec0 11680 101 2 0x00000000 Workqueue: netns cleanup_net ffff8802206939e8 0000000000000096 ffff88022067cec0 00000000001d5f00 ffff880220693fd8 00000000001d5f00 ffff880223263480 ffff88022067cec0 ffffffff82c51d60 7fffffffffffffff ffffffff81ee2698 ffffffff81ee2690 Call Trace: [] schedule+0x29/0x70 [] schedule_timeout+0x26c/0x410 [] ? native_sched_clock+0x2a/0xa0 [] ? mark_held_locks+0x7c/0xb0 [] ? _raw_spin_unlock_irq+0x30/0x50 [] ? trace_hardirqs_on_caller+0x15d/0x200 [] wait_for_completion+0x10c/0x150 [] ? wake_up_state+0x20/0x20 [] _rcu_barrier+0x159/0x200 [] rcu_barrier+0x15/0x20 [] netdev_run_todo+0x6f/0x310 [] ? rollback_registered_many+0x265/0x2e0 [] rtnl_unlock+0xe/0x10 [] default_device_exit_batch+0x156/0x180 [] ? abort_exclusive_wait+0xb0/0xb0 [] ops_exit_list.isra.1+0x53/0x60 [] cleanup_net+0x100/0x1f0 [] process_one_work+0x218/0x850 [] ? process_one_work+0x17f/0x850 [] ? worker_thread+0xe7/0x4a0 [] worker_thread+0x6b/0x4a0 [] ? process_one_work+0x850/0x850 [] kthread+0x10b/0x130 [] ? sched_clock+0x9/0x10 [] ? kthread_create_on_node+0x250/0x250 [] ret_from_fork+0x7c/0xb0 [] ? kthread_create_on_node+0x250/0x250 4 locks held by kworker/u16:6/101: #0: ("%s""netns"){.+.+.+}, at: [] process_one_work+0x17f/0x850 #1: (net_cleanup_work){+.+.+.}, at: [] process_one_work+0x17f/0x850 #2: (net_mutex){+.+.+.}, at: [] cleanup_net+0x8c/0x1f0 #3: (rcu_sched_state.barrier_mutex){+.+...}, at: [] _rcu_barrier+0x35/0x200 INFO: task modprobe:1139 blocked for more than 120 seconds. Not tainted 3.18.0-0.rc1.git2.3.fc22.x86_64 #1 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. modprobe D ffff880213ac1a40 13112 1139 1138 0x00000080 ffff880036ab3be8 0000000000000096 ffff880213ac1a40 00000000001d5f00 ffff880036ab3fd8 00000000001d5f00 ffff880223264ec0 ffff880213ac1a40 ffff880213ac1a40 ffffffff81f8fb48 0000000000000246 ffff880213ac1a40 Call Trace: [] schedule_preempt_disabled+0x31/0x80 [] mutex_lock_nested+0x183/0x440 [] ? register_pernet_subsys+0x1f/0x50 [] ? register_pernet_subsys+0x1f/0x50 [] ? 0xffffffffa06f3000 [] register_pernet_subsys+0x1f/0x50 [] br_init+0x48/0xd3 [bridge] [] do_one_initcall+0xd8/0x210 [] load_module+0x20c2/0x2870 [] ? store_uevent+0x70/0x70 [] ? lock_release_non_nested+0x3c6/0x3d0 [] SyS_init_module+0xe7/0x140 [] system_call_fastpath+0x12/0x17 1 lock held by modprobe/1139: #0: (net_mutex){+.+.+.}, at: [] register_pernet_subsys+0x1f/0x50 INFO: task modprobe:1209 blocked for more than 120 seconds. Not tainted 3.18.0-0.rc1.git2.3.fc22.x86_64 #1 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. modprobe D ffff8800c5324ec0 13368 1209 1151 0x00000080 ffff88020d14bbe8 0000000000000096 ffff8800c5324ec0 00000000001d5f00 ffff88020d14bfd8 00000000001d5f00 ffff880223280000 ffff8800c5324ec0 ffff8800c5324ec0 ffffffff81f8fb48 0000000000000246 ffff8800c5324ec0 Call Trace: [] schedule_preempt_disabled+0x31/0x80 [] mutex_lock_nested+0x183/0x440 [] ? register_pernet_device+0x1d/0x70 [] ? register_pernet_device+0x1d/0x70 [] ? 0xffffffffa070f000 [] register_pernet_device+0x1d/0x70 [] ppp_init+0x20/0x1000 [ppp_generic] [] do_one_initcall+0xd8/0x210 [] load_module+0x20c2/0x2870 [] ? store_uevent+0x70/0x70 [] ? lock_release_non_nested+0x3c6/0x3d0 [] SyS_init_module+0xe7/0x140 [] system_call_fastpath+0x12/0x17 1 lock held by modprobe/1209: #0: (net_mutex){+.+.+.}, at: [] register_pernet_device+0x1d/0x70 > Thanx, Paul > > --------------------------------------------------------------------- > --- > > rcu: More on deadlock between CPU hotplug and expedited grace periods > > Commit dd56af42bd82 (rcu: Eliminate deadlock between CPU hotplug and > expedited grace periods) was incomplete. Although it did eliminate > deadlocks involving synchronize_sched_expedited()'s acquisition of > cpu_hotplug.lock via get_online_cpus(), it did nothing about the > similar > deadlock involving acquisition of this same lock via > put_online_cpus(). > This deadlock became apparent with testing involving hibernation. > > This commit therefore changes put_online_cpus() acquisition of this > lock > to be conditional, and increments a new cpu_hotplug.puts_pending > field > in case of acquisition failure. Then cpu_hotplug_begin() checks for > this > new field being non-zero, and applies any changes to > cpu_hotplug.refcount. > > Reported-by: Jiri Kosina > Signed-off-by: Paul E. McKenney > Tested-by: Jiri Kosina > > diff --git a/kernel/cpu.c b/kernel/cpu.c > index 356450f09c1f..90a3d017b90c 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -64,6 +64,8 @@ static struct { > * an ongoing cpu hotplug operation. > */ > int refcount; > + /* And allows lockless put_online_cpus(). */ > + atomic_t puts_pending; > > #ifdef CONFIG_DEBUG_LOCK_ALLOC > struct lockdep_map dep_map; > @@ -113,7 +115,11 @@ void put_online_cpus(void) > { > if (cpu_hotplug.active_writer == current) > return; > - mutex_lock(&cpu_hotplug.lock); > + if (!mutex_trylock(&cpu_hotplug.lock)) { > + atomic_inc(&cpu_hotplug.puts_pending); > + cpuhp_lock_release(); > + return; > + } > > if (WARN_ON(!cpu_hotplug.refcount)) > cpu_hotplug.refcount++; /* try to fix things up */ > @@ -155,6 +161,12 @@ void cpu_hotplug_begin(void) > cpuhp_lock_acquire(); > for (;;) { > mutex_lock(&cpu_hotplug.lock); > + if (atomic_read(&cpu_hotplug.puts_pending)) { > + int delta; > + > + delta = atomic_xchg(&cpu_hotplug.puts_pending, 0); > + cpu_hotplug.refcount -= delta; > + } > if (likely(!cpu_hotplug.refcount)) > break; > __set_current_state(TASK_UNINTERRUPTIBLE); > > -- 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/