Messages in this thread Patch in this message |  | | Subject | Re: localed stuck in recent 3.18 git in copy_net_ns? | From | Yanko Kaneti <> | Date | Thu, 23 Oct 2014 09:09:26 +0300 |
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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 > > > <paulmck@linux.vnet.ibm.com> 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: [<ffffffff8185e289>] schedule+0x29/0x70 [<ffffffff818634ac>] schedule_timeout+0x26c/0x410 [<ffffffff81028c4a>] ? native_sched_clock+0x2a/0xa0 [<ffffffff81107afc>] ? mark_held_locks+0x7c/0xb0 [<ffffffff81864530>] ? _raw_spin_unlock_irq+0x30/0x50 [<ffffffff81107c8d>] ? trace_hardirqs_on_caller+0x15d/0x200 [<ffffffff8185fcbc>] wait_for_completion+0x10c/0x150 [<ffffffff810e5430>] ? wake_up_state+0x20/0x20 [<ffffffff8112a799>] _rcu_barrier+0x159/0x200 [<ffffffff8112a895>] rcu_barrier+0x15/0x20 [<ffffffff81718f0f>] netdev_run_todo+0x6f/0x310 [<ffffffff8170dad5>] ? rollback_registered_many+0x265/0x2e0 [<ffffffff81725f7e>] rtnl_unlock+0xe/0x10 [<ffffffff8170f936>] default_device_exit_batch+0x156/0x180 [<ffffffff810fd8f0>] ? abort_exclusive_wait+0xb0/0xb0 [<ffffffff817079e3>] ops_exit_list.isra.1+0x53/0x60 [<ffffffff81708590>] cleanup_net+0x100/0x1f0 [<ffffffff810ccff8>] process_one_work+0x218/0x850 [<ffffffff810ccf5f>] ? process_one_work+0x17f/0x850 [<ffffffff810cd717>] ? worker_thread+0xe7/0x4a0 [<ffffffff810cd69b>] worker_thread+0x6b/0x4a0 [<ffffffff810cd630>] ? process_one_work+0x850/0x850 [<ffffffff810d39eb>] kthread+0x10b/0x130 [<ffffffff81028cc9>] ? sched_clock+0x9/0x10 [<ffffffff810d38e0>] ? kthread_create_on_node+0x250/0x250 [<ffffffff8186527c>] ret_from_fork+0x7c/0xb0 [<ffffffff810d38e0>] ? kthread_create_on_node+0x250/0x250 4 locks held by kworker/u16:6/101: #0: ("%s""netns"){.+.+.+}, at: [<ffffffff810ccf5f>] process_one_work+0x17f/0x850 #1: (net_cleanup_work){+.+.+.}, at: [<ffffffff810ccf5f>] process_one_work+0x17f/0x850 #2: (net_mutex){+.+.+.}, at: [<ffffffff8170851c>] cleanup_net+0x8c/0x1f0 #3: (rcu_sched_state.barrier_mutex){+.+...}, at: [<ffffffff8112a675>] _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: [<ffffffff8185e831>] schedule_preempt_disabled+0x31/0x80 [<ffffffff81860083>] mutex_lock_nested+0x183/0x440 [<ffffffff817083af>] ? register_pernet_subsys+0x1f/0x50 [<ffffffff817083af>] ? register_pernet_subsys+0x1f/0x50 [<ffffffffa06f3000>] ? 0xffffffffa06f3000 [<ffffffff817083af>] register_pernet_subsys+0x1f/0x50 [<ffffffffa06f3048>] br_init+0x48/0xd3 [bridge] [<ffffffff81002148>] do_one_initcall+0xd8/0x210 [<ffffffff81153c52>] load_module+0x20c2/0x2870 [<ffffffff8114ec30>] ? store_uevent+0x70/0x70 [<ffffffff8110ac76>] ? lock_release_non_nested+0x3c6/0x3d0 [<ffffffff811544e7>] SyS_init_module+0xe7/0x140 [<ffffffff81865329>] system_call_fastpath+0x12/0x17 1 lock held by modprobe/1139: #0: (net_mutex){+.+.+.}, at: [<ffffffff817083af>] 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: [<ffffffff8185e831>] schedule_preempt_disabled+0x31/0x80 [<ffffffff81860083>] mutex_lock_nested+0x183/0x440 [<ffffffff817083fd>] ? register_pernet_device+0x1d/0x70 [<ffffffff817083fd>] ? register_pernet_device+0x1d/0x70 [<ffffffffa070f000>] ? 0xffffffffa070f000 [<ffffffff817083fd>] register_pernet_device+0x1d/0x70 [<ffffffffa070f020>] ppp_init+0x20/0x1000 [ppp_generic] [<ffffffff81002148>] do_one_initcall+0xd8/0x210 [<ffffffff81153c52>] load_module+0x20c2/0x2870 [<ffffffff8114ec30>] ? store_uevent+0x70/0x70 [<ffffffff8110ac76>] ? lock_release_non_nested+0x3c6/0x3d0 [<ffffffff811544e7>] SyS_init_module+0xe7/0x140 [<ffffffff81865329>] system_call_fastpath+0x12/0x17 1 lock held by modprobe/1209: #0: (net_mutex){+.+.+.}, at: [<ffffffff817083fd>] 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 <jkosina@suse.cz> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > Tested-by: Jiri Kosina <jkosina@suse.cz> > > 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); > >
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