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: Thu, 23 Oct 2014 15:04:06 -0700 Message-ID: <20141023220406.GJ4977@linux.vnet.ibm.com> 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> Reply-To: paulmck@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" To: Yanko Kaneti Return-path: Content-Disposition: inline In-Reply-To: <1414100740.2065.2.camel@declera.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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())? Thanx, Paul