On Thu, Nov 10, 2016 at 9:24 PM, Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote: > On Thu, Nov 10, 2016 at 09:37:47AM -0800, Cong Wang wrote: >> (Cc'ing Paul) >> >> On Wed, Nov 9, 2016 at 7:42 AM, Rolf Neugebauer >> <rolf.neugeba...@docker.com> wrote: >> > Hi >> > >> > We noticed some long delays starting docker containers on some newer >> > kernels (starting with 4.5.x and still present in 4.9-rc4, 4.4.x is >> > fine). We narrowed this down to the creation of a network namespace >> > being delayed directly after removing another one (details and >> > reproduction below). We have seen delays of up to 60s on some systems. >> > >> > - The delay is proportional to the number of CPUs (online or offline). >> > We first discovered it with a Hyper-V Linux VM. Hyper-V advertises up >> > to 240 offline vCPUs even if one configures the VM with only, say 2 >> > vCPUs. We see linear increase in delay when we change NR_CPUS in the >> > kernel config. >> > >> > - The delay is also dependent on some tunnel network interfaces being >> > present (which we had compiled in in one of our kernel configs). >> > >> > - We can reproduce this issue with stock kernels from >> > http://kernel.ubuntu.com/~kernel-ppa/mainline/running in Hyper-V VMs >> > as well as other hypervisors like qemu and hyperkit where we have good >> > control over the number of CPUs. >> > >> > A simple test is: >> > modprobe ipip >> > moprobe ip_gre >> > modprobe ip_vti >> > echo -n "add netns foo ===> "; /usr/bin/time -f "%E" ip netns add foo >> > echo -n "del netns foo ===> "; /usr/bin/time -f "%E" ip netns delete foo >> > echo -n "add netns bar ===> "; /usr/bin/time -f "%E" ip netns add bar >> > echo -n "del netns bar ===> "; /usr/bin/time -f "%E" ip netns delete bar >> > >> > with an output like: >> > add netns foo ===> 0:00.00 >> > del netns foo ===> 0:00.01 >> > add netns bar ===> 0:08.53 >> > del netns bar ===> 0:00.01 >> > >> > This is on a 4.9-rc4 kernel from the above URL configured with >> > NR_CPUS=256 running in a Hyper-V VM (kernel config attached). >> > >> > Below is a dump of the work queues while the second 'ip add netns' is >> > hanging. The state of the work queues does not seem to change while >> > the command is delayed and the pattern shown is consistent across >> > different kernel versions. >> > >> > Is this a known issue and/or is someone working on a fix? >> >> Not to me. >> >> >> > >> > [ 610.356272] sysrq: SysRq : Show Blocked State >> > [ 610.356742] task PC stack pid father >> > [ 610.357252] kworker/u480:1 D 0 1994 2 0x00000000 >> > [ 610.357752] Workqueue: netns cleanup_net >> > [ 610.358239] ffff9892f1065800 0000000000000000 ffff9892ee1e1e00 >> > ffff9892f8e59340 >> > [ 610.358705] ffff9892f4526900 ffffbf0104b5ba88 ffffffffbe486df3 >> > ffffbf0104b5ba60 >> > [ 610.359168] 00ffffffbdcbe663 ffff9892f8e59340 0000000100012e70 >> > ffff9892ee1e1e00 >> > [ 610.359677] Call Trace: >> > [ 610.360169] [<ffffffffbe486df3>] ? __schedule+0x233/0x6e0 >> > [ 610.360723] [<ffffffffbe4872d6>] schedule+0x36/0x80 >> > [ 610.361194] [<ffffffffbe48a9ca>] schedule_timeout+0x22a/0x3f0 >> > [ 610.361789] [<ffffffffbe486dfb>] ? __schedule+0x23b/0x6e0 >> > [ 610.362260] [<ffffffffbe487d24>] wait_for_completion+0xb4/0x140 >> > [ 610.362736] [<ffffffffbdcb05a0>] ? wake_up_q+0x80/0x80 >> > [ 610.363306] [<ffffffffbdceb528>] __wait_rcu_gp+0xc8/0xf0 >> > [ 610.363782] [<ffffffffbdceea5c>] synchronize_sched+0x5c/0x80 >> > [ 610.364137] [<ffffffffbdcf0010>] ? call_rcu_bh+0x20/0x20 >> > [ 610.364742] [<ffffffffbdceb440>] ? >> > trace_raw_output_rcu_utilization+0x60/0x60 >> > [ 610.365337] [<ffffffffbe3696bc>] synchronize_net+0x1c/0x30 >> >> This is a worker which holds the net_mutex and is waiting for >> a RCU grace period to elapse. >> >> >> > [ 610.365846] [<ffffffffbe369803>] netif_napi_del+0x23/0x80 >> > [ 610.367494] [<ffffffffc057f6f8>] ip_tunnel_dev_free+0x68/0xf0 >> > [ip_tunnel] >> > [ 610.368007] [<ffffffffbe372c10>] netdev_run_todo+0x230/0x330 >> > [ 610.368454] [<ffffffffbe37eb4e>] rtnl_unlock+0xe/0x10 >> > [ 610.369001] [<ffffffffc057f4df>] ip_tunnel_delete_net+0xdf/0x120 >> > [ip_tunnel] >> > [ 610.369500] [<ffffffffc058b92c>] ipip_exit_net+0x2c/0x30 [ipip] >> > [ 610.369997] [<ffffffffbe362688>] ops_exit_list.isra.4+0x38/0x60 >> > [ 610.370636] [<ffffffffbe363674>] cleanup_net+0x1c4/0x2b0 >> > [ 610.371130] [<ffffffffbdc9e4ac>] process_one_work+0x1fc/0x4b0 >> > [ 610.371812] [<ffffffffbdc9e7ab>] worker_thread+0x4b/0x500 >> > [ 610.373074] [<ffffffffbdc9e760>] ? process_one_work+0x4b0/0x4b0 >> > [ 610.373622] [<ffffffffbdc9e760>] ? process_one_work+0x4b0/0x4b0 >> > [ 610.374100] [<ffffffffbdca4b09>] kthread+0xd9/0xf0 >> > [ 610.374574] [<ffffffffbdca4a30>] ? kthread_park+0x60/0x60 >> > [ 610.375198] [<ffffffffbe48c2b5>] ret_from_fork+0x25/0x30 >> > [ 610.375678] ip D 0 2149 2148 0x00000000 >> > [ 610.376185] ffff9892f0a99000 0000000000000000 ffff9892f0a66900 >> > [ 610.376185] ffff9892f8e59340 >> > [ 610.376185] ffff9892f4526900 ffffbf0101173db8 ffffffffbe486df3 >> > [ 610.376753] 00000005fecffd76 >> > [ 610.376762] 00ff9892f11d9820 ffff9892f8e59340 ffff989200000000 >> > ffff9892f0a66900 >> > [ 610.377274] Call Trace: >> > [ 610.377789] [<ffffffffbe486df3>] ? __schedule+0x233/0x6e0 >> > [ 610.378306] [<ffffffffbe4872d6>] schedule+0x36/0x80 >> > [ 610.378992] [<ffffffffbe48756e>] schedule_preempt_disabled+0xe/0x10 >> > [ 610.379514] [<ffffffffbe489199>] __mutex_lock_slowpath+0xb9/0x130 >> > [ 610.380031] [<ffffffffbde0fce2>] ? __kmalloc+0x162/0x1e0 >> > [ 610.380556] [<ffffffffbe48922f>] mutex_lock+0x1f/0x30 >> > [ 610.381135] [<ffffffffbe3637ff>] copy_net_ns+0x9f/0x170 >> > [ 610.381647] [<ffffffffbdca5e6b>] create_new_namespaces+0x11b/0x200 >> > [ 610.382249] [<ffffffffbdca60fa>] unshare_nsproxy_namespaces+0x5a/0xb0 >> > [ 610.382818] [<ffffffffbdc82dcd>] SyS_unshare+0x1cd/0x360 >> > [ 610.383319] [<ffffffffbe48c03b>] entry_SYSCALL_64_fastpath+0x1e/0xad >> >> This process is apparently waiting for the net_mutex held by the previous >> one. >> >> Either RCU implementation is broken or something else is missing. >> Do you have more stack traces of related processes? For example, >> rcu_tasks_kthread. And if anything you can help to narrow down the problem, >> it would be great. > > Did you set the rcu_normal boot parameter? Doing so would have this effect. > > (It is intended for real-time users who don't like expedited grace periods.)
rcu_normal is not set on the kernel command line and /sys/kernel/rcu_normal and /sys/kernel/rcu_expedited both show 0. > > Thanx, Paul >
