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Subjectsched/timekeeping: lockdep spew
Hi all,

I've stumbled on this spew inside a KVM tools guest running latest -next kernel:


[ 251.100221] ======================================================
[ 251.100221] [ INFO: possible circular locking dependency detected ]
[ 251.100221] 3.13.0-rc2-next-20131206-sasha-00005-g8be2375-dirty #4053 Not tainted
[ 251.101967] -------------------------------------------------------
[ 251.101967] kworker/10:1/4506 is trying to acquire lock:
[ 251.101967] (timekeeper_seq){----..}, at: [<ffffffff81160e96>] retrigger_next_event+0x56/0x70
[ 251.101967]
[ 251.101967] but task is already holding lock:
[ 251.101967] (hrtimer_bases.lock#11){-.-...}, at: [<ffffffff81160e7c>] retrigger_next_event+0x3c/0x70
[ 251.101967]
[ 251.101967] which lock already depends on the new lock.
[ 251.101967]
[ 251.101967]
[ 251.101967] the existing dependency chain (in reverse order) is:
[ 251.101967]
-> #5 (hrtimer_bases.lock#11){-.-...}:
[ 251.101967] [<ffffffff81194803>] validate_chain+0x6c3/0x7b0
[ 251.101967] [<ffffffff81194d9d>] __lock_acquire+0x4ad/0x580
[ 251.101967] [<ffffffff81194ff2>] lock_acquire+0x182/0x1d0
[ 251.101967] [<ffffffff84398500>] _raw_spin_lock+0x40/0x80
[ 251.101967] [<ffffffff81161828>] __hrtimer_start_range_ns+0x208/0x4c0
[ 251.101967] [<ffffffff8116a910>] start_bandwidth_timer+0x50/0x60
[ 251.101967] [<ffffffff8118430e>] __enqueue_rt_entity+0x23e/0x290
[ 251.101967] [<ffffffff811846db>] enqueue_rt_entity+0x6b/0x80
[ 251.101967] [<ffffffff81184726>] enqueue_task_rt+0x36/0xb0
[ 251.101967] [<ffffffff8116af42>] enqueue_task+0x52/0x60
[ 251.101967] [<ffffffff8116af72>] activate_task+0x22/0x30
[ 251.101967] [<ffffffff8116afa1>] ttwu_activate+0x21/0x50
[ 251.101967] [<ffffffff8116b00c>] T.2138+0x3c/0x60
[ 251.101967] [<ffffffff8116b0e6>] ttwu_queue+0xb6/0xe0
[ 251.101967] [<ffffffff81172b34>] try_to_wake_up+0x264/0x2a0
[ 251.101967] [<ffffffff81172bef>] wake_up_process+0x3f/0x50
[ 251.101967] [<ffffffff81202cac>] watchdog_timer_fn+0x4c/0x1b0
[ 251.101967] [<ffffffff81161d16>] __run_hrtimer+0x1f6/0x310
[ 251.101967] [<ffffffff81161fc6>] hrtimer_run_queues+0x196/0x1d0
[ 251.101967] [<ffffffff811402de>] run_local_timers+0xe/0x20
[ 251.101967] [<ffffffff8114032d>] update_process_times+0x3d/0x80
[ 251.101967] [<ffffffff811cbddb>] tick_periodic+0xab/0xc0
[ 251.101967] [<ffffffff811cbe14>] tick_handle_periodic+0x24/0x80
[ 251.101967] [<ffffffff810a760d>] local_apic_timer_interrupt+0x5d/0x70
[ 251.101967] [<ffffffff843a4de5>] smp_apic_timer_interrupt+0x45/0x60
[ 251.101967] [<ffffffff843a3732>] apic_timer_interrupt+0x72/0x80
[ 251.101967] [<ffffffff81077ecd>] default_idle+0x11d/0x260
[ 251.101967] [<ffffffff81077398>] arch_cpu_idle+0x18/0x50
[ 251.101967] [<ffffffff811a9211>] cpu_idle_loop+0x351/0x460
[ 251.101967] [<ffffffff811a9390>] cpu_startup_entry+0x70/0x80
[ 251.101967] [<ffffffff810a5263>] start_secondary+0xf3/0x100
[ 251.101967]
-> #4 (&rt_b->rt_runtime_lock){-.-...}:
[ 251.101967] [<ffffffff81194803>] validate_chain+0x6c3/0x7b0
[ 251.101967] [<ffffffff81194d9d>] __lock_acquire+0x4ad/0x580
[ 251.101967] [<ffffffff81194ff2>] lock_acquire+0x182/0x1d0
[ 251.101967] [<ffffffff84398500>] _raw_spin_lock+0x40/0x80
[ 251.101967] [<ffffffff811842f9>] __enqueue_rt_entity+0x229/0x290
[ 251.101967] [<ffffffff811846db>] enqueue_rt_entity+0x6b/0x80
[ 251.101967] [<ffffffff81184726>] enqueue_task_rt+0x36/0xb0
[ 251.101967] [<ffffffff8116af42>] enqueue_task+0x52/0x60
[ 251.101967] [<ffffffff81171ebb>] __sched_setscheduler+0x33b/0x3f0
[ 251.101967] [<ffffffff81171f80>] sched_setscheduler_nocheck+0x10/0x20
[ 251.101967] [<ffffffff811b5e2b>] rcu_cpu_kthread_setup+0x2b/0x30
[ 251.101967] [<ffffffff81166efd>] smpboot_thread_fn+0x1ed/0x2c0
[ 251.101967] [<ffffffff8115d9e5>] kthread+0x105/0x110
[ 251.101967] [<ffffffff843a297c>] ret_from_fork+0x7c/0xb0
[ 251.101967]
-> #3 (&rq->lock){-.-.-.}:
[ 251.101967] [<ffffffff81194803>] validate_chain+0x6c3/0x7b0
[ 251.101967] [<ffffffff81194d9d>] __lock_acquire+0x4ad/0x580
[ 251.101967] [<ffffffff81194ff2>] lock_acquire+0x182/0x1d0
[ 251.101967] [<ffffffff84398500>] _raw_spin_lock+0x40/0x80
[ 251.101967] [<ffffffff8116f489>] wake_up_new_task+0x149/0x270
[ 251.101967] [<ffffffff8113002a>] do_fork+0x1ba/0x270
[ 251.101967] [<ffffffff81130166>] kernel_thread+0x26/0x30
[ 251.101967] [<ffffffff84387c16>] rest_init+0x26/0x150
[ 251.101967] [<ffffffff87068377>] start_kernel+0x3b9/0x3c0
[ 251.101967] [<ffffffff870673d9>] x86_64_start_reservations+0x2a/0x2c
[ 251.101967] [<ffffffff870675ae>] x86_64_start_kernel+0x186/0x195
[ 251.101967]
-> #2 (&p->pi_lock){-.-.-.}:
[ 251.101967] [<ffffffff81194803>] validate_chain+0x6c3/0x7b0
[ 251.101967] [<ffffffff81194d9d>] __lock_acquire+0x4ad/0x580
[ 251.101967] [<ffffffff81194ff2>] lock_acquire+0x182/0x1d0
[ 251.101967] [<ffffffff843986b1>] _raw_spin_lock_irqsave+0x91/0xd0
[ 251.101967] [<ffffffff81172909>] try_to_wake_up+0x39/0x2a0
[ 251.101967] [<ffffffff81172bef>] wake_up_process+0x3f/0x50
[ 251.101967] [<ffffffff811507da>] start_worker+0x2a/0x40
[ 251.101967] [<ffffffff81156a9d>] create_and_start_worker+0x4d/0x90
[ 251.101967] [<ffffffff8708ecec>] init_workqueues+0x192/0x3cb
[ 251.101967] [<ffffffff810020ca>] do_one_initcall+0xca/0x1e0
[ 251.101967] [<ffffffff87067cf1>] kernel_init_freeable+0x2b4/0x354
[ 251.101967] [<ffffffff84387d4e>] kernel_init+0xe/0x130
[ 251.101967] [<ffffffff843a297c>] ret_from_fork+0x7c/0xb0
[ 251.101967]
-> #1 (&(&pool->lock)->rlock){-.-...}:
[ 251.101967] [<ffffffff81194803>] validate_chain+0x6c3/0x7b0
[ 251.101967] [<ffffffff81194d9d>] __lock_acquire+0x4ad/0x580
[ 251.101967] [<ffffffff81194ff2>] lock_acquire+0x182/0x1d0
[ 251.101967] [<ffffffff84398500>] _raw_spin_lock+0x40/0x80
[ 251.101967] [<ffffffff81153e69>] __queue_work+0x1a9/0x3f0
[ 251.101967] [<ffffffff81154168>] queue_work_on+0x98/0x120
[ 251.101967] [<ffffffff81161351>] clock_was_set_delayed+0x21/0x30
[ 251.101967] [<ffffffff811c4bd1>] do_adjtimex+0x111/0x160
[ 251.101967] [<ffffffff811e2711>] compat_sys_adjtimex+0x41/0x70
[ 251.101967] [<ffffffff843a4b49>] ia32_sysret+0x0/0x5
[ 251.101967]
-> #0 (timekeeper_seq){----..}:
[ 251.101967] [<ffffffff81193d2f>] check_prev_add+0x13f/0x550
[ 251.101967] [<ffffffff81194803>] validate_chain+0x6c3/0x7b0
[ 251.101967] [<ffffffff81194d9d>] __lock_acquire+0x4ad/0x580
[ 251.101967] [<ffffffff81194ff2>] lock_acquire+0x182/0x1d0
[ 251.101967] [<ffffffff811c590a>] ktime_get_update_offsets+0x9a/0x1e0
[ 251.101967] [<ffffffff81160e96>] retrigger_next_event+0x56/0x70
[ 251.101967] [<ffffffff811d5999>] on_each_cpu+0x89/0x120
[ 251.101967] [<ffffffff8116130c>] clock_was_set+0x1c/0x30
[ 251.101967] [<ffffffff8116132e>] clock_was_set_work+0xe/0x10
[ 251.101967] [<ffffffff81154a80>] process_one_work+0x320/0x530
[ 251.101967] [<ffffffff81157005>] worker_thread+0x215/0x350
[ 251.101967] [<ffffffff8115d9e5>] kthread+0x105/0x110
[ 251.101967] [<ffffffff843a297c>] ret_from_fork+0x7c/0xb0
[ 251.101967]
[ 251.101967] other info that might help us debug this:
[ 251.101967]
[ 251.101967] Chain exists of:
timekeeper_seq --> &rt_b->rt_runtime_lock --> hrtimer_bases.lock#11

[ 251.101967] Possible unsafe locking scenario:
[ 251.101967]
[ 251.101967] CPU0 CPU1
[ 251.101967] ---- ----
[ 251.101967] lock(hrtimer_bases.lock#11);
[ 251.101967] lock(&rt_b->rt_runtime_lock);
[ 251.101967] lock(hrtimer_bases.lock#11);
[ 251.101967] lock(timekeeper_seq);
[ 251.101967]
[ 251.101967] *** DEADLOCK ***
[ 251.101967]
[ 251.101967] 3 locks held by kworker/10:1/4506:
[ 251.101967] #0: (events){.+.+.+}, at: [<ffffffff81154960>] process_one_work+0x200/0x530
[ 251.101967] #1: (hrtimer_work){+.+...}, at: [<ffffffff81154960>] process_one_work+0x200/0x530
[ 251.101967] #2: (hrtimer_bases.lock#11){-.-...}, at: [<ffffffff81160e7c>]
retrigger_next_event+0x3c/0x70
[ 251.101967]
[ 251.101967] stack backtrace:
[ 251.101967] CPU: 10 PID: 4506 Comm: kworker/10:1 Not tainted
3.13.0-rc2-next-20131206-sasha-00005-g8be2375-dirty #4053
[ 251.101967] Workqueue: events clock_was_set_work
[ 251.101967] 0000000000000000 ffff880fb9c13a18 ffffffff84391b37 0000000000000000
[ 251.101967] 0000000000000000 ffff880fb9c13a68 ffffffff811918d9 ffff880fb9c13a88
[ 251.101967] ffffffff875fb100 ffff880fb9c13a68 ffff880fcacf8c48 ffff880fcacf8c80
[ 251.101967] Call Trace:
[ 251.101967] [<ffffffff84391b37>] dump_stack+0x52/0x7f
[ 251.101967] [<ffffffff811918d9>] print_circular_bug+0x129/0x160
[ 251.101967] [<ffffffff81193d2f>] check_prev_add+0x13f/0x550
[ 251.101967] [<ffffffff8118ed1d>] ? T.1062+0x9d/0xb0
[ 251.101967] [<ffffffff81194803>] validate_chain+0x6c3/0x7b0
[ 251.101967] [<ffffffff81175588>] ? sched_clock_cpu+0x108/0x120
[ 251.101967] [<ffffffff81194d9d>] __lock_acquire+0x4ad/0x580
[ 251.101967] [<ffffffff81194ff2>] lock_acquire+0x182/0x1d0
[ 251.101967] [<ffffffff81160e96>] ? retrigger_next_event+0x56/0x70
[ 251.101967] [<ffffffff81190ea2>] ? __lock_acquired+0x2a2/0x2e0
[ 251.101967] [<ffffffff811c590a>] ktime_get_update_offsets+0x9a/0x1e0
[ 251.101967] [<ffffffff81160e96>] ? retrigger_next_event+0x56/0x70
[ 251.101967] [<ffffffff81160e96>] retrigger_next_event+0x56/0x70
[ 251.101967] [<ffffffff81160e40>] ? hrtimer_wakeup+0x30/0x30
[ 251.101967] [<ffffffff811d5999>] on_each_cpu+0x89/0x120
[ 251.101967] [<ffffffff8116130c>] clock_was_set+0x1c/0x30
[ 251.101967] [<ffffffff8116132e>] clock_was_set_work+0xe/0x10
[ 251.101967] [<ffffffff81154a80>] process_one_work+0x320/0x530
[ 251.101967] [<ffffffff81154960>] ? process_one_work+0x200/0x530
[ 251.101967] [<ffffffff81157005>] worker_thread+0x215/0x350
[ 251.101967] [<ffffffff81156df0>] ? manage_workers+0x180/0x180
[ 251.101967] [<ffffffff8115d9e5>] kthread+0x105/0x110
[ 251.101967] [<ffffffff8115d8e0>] ? set_kthreadd_affinity+0x30/0x30
[ 251.101967] [<ffffffff843a297c>] ret_from_fork+0x7c/0xb0
[ 251.101967] [<ffffffff8115d8e0>] ? set_kthreadd_affinity+0x30/0x30


Thanks,
Sasha


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