From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jay Vosburgh Subject: Re: localed stuck in recent 3.18 git in copy_net_ns? Date: Thu, 23 Oct 2014 21:48:34 -0700 Message-ID: <31920.1414126114@famine> References: <20141022185511.GI4977@linux.vnet.ibm.com> <20141022224032.GA1240@declera.com> <20141022232421.GN4977@linux.vnet.ibm.com> <1414044566.2031.1.camel@declera.com> <20141023122750.GP4977@linux.vnet.ibm.com> <20141023153333.GA19278@linux.vnet.ibm.com> <20141023195159.GA2331@declera.com> <20141023200507.GC4977@linux.vnet.ibm.com> <1414100740.2065.2.camel@declera.com> <20141023220406.GJ4977@linux.vnet.ibm.com> Cc: Yanko Kaneti , Josh Boyer , "Eric W. Biederman" , Cong Wang , Kevin Fenzi , netdev , "Linux-Kernel@Vger. Kernel. Org" To: paulmck@linux.vnet.ibm.com Return-path: In-reply-to: <20141023220406.GJ4977@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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: >> > > On Thu-10/23/14-2014 08:33, Paul E. McKenney wrote: >> > > > On Thu, Oct 23, 2014 at 05:27:50AM -0700, Paul E. McKenney wrote: >> > > > > On Thu, Oct 23, 2014 at 09:09:26AM +0300, Yanko Kaneti wrote: >> > > > > > 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 >> > > > > >> > > > > Well, I was hoping. I will take a closer look at the RCU >> > > > > merge commit >> > > > > and see what suggests itself. I am likely to ask you to >> > > > > revert specific >> > > > > commits, if that works for you. >> > > > >> > > > Well, rather than reverting commits, could you please try >> > > > testing the >> > > > following commits? >> > > > >> > > > 11ed7f934cb8 (rcu: Make nocb leader kthreads process pending >> > > > callbacks after spawning) >> > > > >> > > > 73a860cd58a1 (rcu: Replace flush_signals() with >> > > > WARN_ON(signal_pending())) >> > > > >> > > > c847f14217d5 (rcu: Avoid misordering in nocb_leader_wait()) >> > > > >> > > > For whatever it is worth, I am guessing this one. >> > > >> > > Indeed, c847f14217d5 it is. >> > > >> > > Much to my embarrasment I just noticed that in addition to the >> > > rcu merge, triggering the bug "requires" my specific Fedora >> > > rawhide network >> > > setup. Booting in single mode and modprobe ppp_generic is fine. >> > > The bug >> > > appears when starting with my regular fedora network setup, which >> > > in my case >> > > includes 3 ethernet adapters and a libvirt birdge+nat setup. >> > > >> > > Hope that helps. >> > > >> > > I am attaching the config. >> > >> > It does help a lot, thank you!!! >> > >> > The following patch is a bit of a shot in the dark, and assumes that >> > commit 1772947bd012 (rcu: Handle NOCB callbacks from irq-disabled >> > idle >> > code) introduced the problem. Does this patch fix things up? >> >> Unfortunately not, This is linus-tip + patch > >OK. Can't have everything, I guess. > >> INFO: task kworker/u16:6:96 blocked for more than 120 seconds. >> Not tainted 3.18.0-rc1+ #4 >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> kworker/u16:6 D ffff8800ca84cec0 11168 96 2 0x00000000 >> Workqueue: netns cleanup_net >> ffff8802218339e8 0000000000000096 ffff8800ca84cec0 00000000001d5f00 >> ffff880221833fd8 00000000001d5f00 ffff880223264ec0 ffff8800ca84cec0 >> ffffffff82c52040 7fffffffffffffff ffffffff81ee2658 ffffffff81ee2650 >> 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/u16:6/96: >> #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:1045 blocked for more than 120 seconds. >> Not tainted 3.18.0-rc1+ #4 >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> modprobe D ffff880218343480 12920 1045 1044 0x00000080 >> ffff880218353bf8 0000000000000096 ffff880218343480 00000000001d5f00 >> ffff880218353fd8 00000000001d5f00 ffffffff81e1b580 ffff880218343480 >> ffff880218343480 ffffffff81f8f748 0000000000000246 ffff880218343480 >> Call Trace: >> [] schedule_preempt_disabled+0x31/0x80 >> [] mutex_lock_nested+0x183/0x440 >> [] ? register_pernet_subsys+0x1f/0x50 >> [] ? register_pernet_subsys+0x1f/0x50 >> [] ? 0xffffffffa0673000 >> [] register_pernet_subsys+0x1f/0x50 >> [] br_init+0x48/0xd3 [bridge] >> [] do_one_initcall+0xd8/0x210 >> [] load_module+0x20c2/0x2870 >> [] ? store_uevent+0x70/0x70 >> [] ? kernel_read+0x57/0x90 >> [] SyS_finit_module+0xa6/0xe0 >> [] system_call_fastpath+0x12/0x17 >> 1 lock held by modprobe/1045: >> #0: (net_mutex){+.+.+.}, at: [] register_pernet_subsys+0x1f/0x50 > >Presumably the kworker/u16:6 completed, then modprobe hung? > >If not, I have some very hard questions about why net_mutex can be >held by two tasks concurrently, given that it does not appear to be a >reader-writer lock... > >Either way, my patch assumed that 39953dfd4007 (rcu: Avoid misordering in >__call_rcu_nocb_enqueue()) would work and that 1772947bd012 (rcu: Handle >NOCB callbacks from irq-disabled idle code) would fail. Is that the case? >If not, could you please bisect the commits between 11ed7f934cb8 (rcu: >Make nocb leader kthreads process pending callbacks after spawning) >and c847f14217d5 (rcu: Avoid misordering in nocb_leader_wait())? Just a note to add that I am also reliably inducing what appears to be this issue on a current -net tree, when configuring openvswitch via script. I am available to test patches or bisect tomorrow (Friday) US time if needed. The stack is as follows: [ 1320.492020] INFO: task ovs-vswitchd:1303 blocked for more than 120 seconds. [ 1320.498965] Not tainted 3.17.0-testola+ #1 [ 1320.503570] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 1320.511374] ovs-vswitchd D ffff88013fc14600 0 1303 1302 0x00000004 [ 1320.511378] ffff8801388d77d8 0000000000000002 ffff880031144b00 ffff8801388d7fd8 [ 1320.511382] 0000000000014600 0000000000014600 ffff8800b092e400 ffff880031144b00 [ 1320.511385] ffff8800b1126000 ffffffff81c58ad0 ffffffff81c58ad8 7fffffffffffffff [ 1320.511389] Call Trace: [ 1320.511396] [] schedule+0x29/0x70 [ 1320.511399] [] schedule_timeout+0x1dc/0x260 [ 1320.511404] [] ? check_preempt_curr+0x8d/0xa0 [ 1320.511407] [] ? ttwu_do_wakeup+0x1d/0xd0 [ 1320.511410] [] wait_for_completion+0xa6/0x160 [ 1320.511413] [] ? wake_up_state+0x20/0x20 [ 1320.511417] [] _rcu_barrier+0x157/0x200 [ 1320.511419] [] rcu_barrier+0x15/0x20 [ 1320.511423] [] netdev_run_todo+0x60/0x300 [ 1320.511427] [] rtnl_unlock+0xe/0x10 [ 1320.511435] [] internal_dev_destroy+0x55/0x80 [openvswitch] [ 1320.511440] [] ovs_vport_del+0x32/0x40 [openvswitch] [ 1320.511444] [] ovs_dp_detach_port+0x30/0x40 [openvswitch] [ 1320.511448] [] ovs_vport_cmd_del+0xc5/0x110 [openvswitch] [ 1320.511452] [] genl_family_rcv_msg+0x1a5/0x3c0 [ 1320.511455] [] ? genl_family_rcv_msg+0x3c0/0x3c0 [ 1320.511458] [] genl_rcv_msg+0x91/0xd0 [ 1320.511461] [] netlink_rcv_skb+0xc1/0xe0 [ 1320.511463] [] genl_rcv+0x2c/0x40 [ 1320.511466] [] netlink_unicast+0xf6/0x200 [ 1320.511468] [] netlink_sendmsg+0x31d/0x780 [ 1320.511472] [] ? netlink_rcv_wake+0x44/0x60 [ 1320.511475] [] ? netlink_recvmsg+0x1d3/0x3e0 [ 1320.511479] [] sock_sendmsg+0x93/0xd0 [ 1320.511484] [] ? apparmor_file_alloc_security+0x20/0x40 [ 1320.511487] [] ? verify_iovec+0x47/0xd0 [ 1320.511491] [] ___sys_sendmsg+0x399/0x3b0 [ 1320.511495] [] ? kernfs_seq_stop_active+0x32/0x40 [ 1320.511499] [] ? native_sched_clock+0x35/0x90 [ 1320.511502] [] ? native_sched_clock+0x35/0x90 [ 1320.511505] [] ? sched_clock+0x9/0x10 [ 1320.511509] [] ? acct_account_cputime+0x1c/0x20 [ 1320.511512] [] ? account_user_time+0x8b/0xa0 [ 1320.511516] [] ? __fget_light+0x25/0x70 [ 1320.511519] [] __sys_sendmsg+0x42/0x80 [ 1320.511521] [] SyS_sendmsg+0x12/0x20 [ 1320.511525] [] tracesys_phase2+0xd8/0xdd -J --- -Jay Vosburgh, jay.vosburgh@canonical.com