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Subjectyama: lockdep warning on yama_ptracer_del
Hi all,

I was fuzzing with trinity within a KVM tools guest (lkvm) on a linux-next kernel, and got the
following dump which I believe to be noise due to how the timers work - but I'm not 100% sure.

If that's actually noise, the solution would be to get the timer code to assign meaningful
names for it's timer mutexes, right?

[ 954.666095]
[ 954.666471] ======================================================
[ 954.668233] [ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
[ 954.670194] 3.7.0-rc1-next-20121017-sasha-00002-g2353878-dirty #54 Tainted: G W
[ 954.672344] ------------------------------------------------------
[ 954.674123] trinity-child34/8145 [HC0[0]:SC0[2]:HE0:SE0] is trying to acquire:
[ 954.674123] (ptracer_relations_lock){+.....}, at: [<ffffffff8196409d>] yama_ptracer_del+0x1d/0xa0
[ 954.674123]
[ 954.674123] and this task is already holding:
[ 954.674123] (&(&new_timer->it_lock)->rlock){-.-...}, at: [<ffffffff81138340>] exit_itimers+0x50/0x160
[ 954.674123] which would create a new lock dependency:
[ 954.674123] (&(&new_timer->it_lock)->rlock){-.-...} -> (ptracer_relations_lock){+.....}
[ 954.674123]
[ 954.674123] but this new dependency connects a HARDIRQ-irq-safe lock:
[ 954.674123] (&(&new_timer->it_lock)->rlock){-.-...}
... which became HARDIRQ-irq-safe at:
[ 954.674123] [<ffffffff8117f814>] __lock_acquire+0x864/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67e5c>] _raw_spin_lock_irqsave+0x7c/0xc0
[ 954.674123] [<ffffffff811377d2>] posix_timer_fn+0x32/0xd0
[ 954.674123] [<ffffffff8113df49>] __run_hrtimer+0x279/0x4d0
[ 954.674123] [<ffffffff8113eff9>] hrtimer_interrupt+0x109/0x210
[ 954.674123] [<ffffffff810981d5>] smp_apic_timer_interrupt+0x85/0xa0
[ 954.674123] [<ffffffff83a6a6b2>] apic_timer_interrupt+0x72/0x80
[ 954.674123] [<ffffffff81077e55>] default_idle+0x235/0x5b0
[ 954.674123] [<ffffffff81079a38>] cpu_idle+0x138/0x160
[ 954.674123] [<ffffffff839fe5fe>] start_secondary+0x26e/0x276
[ 954.674123]
[ 954.674123] to a HARDIRQ-irq-unsafe lock:
[ 954.674123] (ptracer_relations_lock){+.....}
... which became HARDIRQ-irq-unsafe at:
[ 954.674123] ... [<ffffffff8117f8df>] __lock_acquire+0x92f/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67f70>] _raw_spin_lock_bh+0x40/0x80
[ 954.674123] [<ffffffff8196409d>] yama_ptracer_del+0x1d/0xa0
[ 954.674123] [<ffffffff819644ec>] yama_task_free+0xc/0x10
[ 954.674123] [<ffffffff81923b41>] security_task_free+0x11/0x30
[ 954.674123] [<ffffffff81106ab8>] __put_task_struct+0x68/0x110
[ 954.674123] [<ffffffff8110e6b8>] delayed_put_task_struct+0x118/0x180
[ 954.674123] [<ffffffff811c9739>] rcu_do_batch.isra.14+0x5a9/0xab0
[ 954.674123] [<ffffffff811c9e5a>] rcu_cpu_kthread+0x21a/0x630
[ 954.674123] [<ffffffff81144440>] smpboot_thread_fn+0x2b0/0x2e0
[ 954.674123] [<ffffffff81138b63>] kthread+0xe3/0xf0
[ 954.674123] [<ffffffff83a698bc>] ret_from_fork+0x7c/0xb0
[ 954.674123]
[ 954.674123] other info that might help us debug this:
[ 954.674123]
[ 954.674123] Possible interrupt unsafe locking scenario:
[ 954.674123]
[ 954.674123] CPU0 CPU1
[ 954.674123] ---- ----
[ 954.674123] lock(ptracer_relations_lock);
[ 954.674123] local_irq_disable();
[ 954.674123] lock(&(&new_timer->it_lock)->rlock);
[ 954.674123] lock(ptracer_relations_lock);
[ 954.674123] <Interrupt>
[ 954.674123] lock(&(&new_timer->it_lock)->rlock);
[ 954.674123]
[ 954.674123] *** DEADLOCK ***
[ 954.674123]
[ 954.674123] 1 lock held by trinity-child34/8145:
[ 954.674123] #0: (&(&new_timer->it_lock)->rlock){-.-...}, at: [<ffffffff81138340>] exit_itimers+0x50/0x160
[ 954.674123]
the dependencies between HARDIRQ-irq-safe lock and the holding lock:
[ 954.674123] -> (&(&new_timer->it_lock)->rlock){-.-...} ops: 3138190 {
[ 954.674123] IN-HARDIRQ-W at:
[ 954.674123] [<ffffffff8117f814>] __lock_acquire+0x864/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67e5c>] _raw_spin_lock_irqsave+0x7c/0xc0
[ 954.674123] [<ffffffff811377d2>] posix_timer_fn+0x32/0xd0
[ 954.674123] [<ffffffff8113df49>] __run_hrtimer+0x279/0x4d0
[ 954.674123] [<ffffffff8113eff9>] hrtimer_interrupt+0x109/0x210
[ 954.674123] [<ffffffff810981d5>] smp_apic_timer_interrupt+0x85/0xa0
[ 954.674123] [<ffffffff83a6a6b2>] apic_timer_interrupt+0x72/0x80
[ 954.674123] [<ffffffff81077e55>] default_idle+0x235/0x5b0
[ 954.674123] [<ffffffff81079a38>] cpu_idle+0x138/0x160
[ 954.674123] [<ffffffff839fe5fe>] start_secondary+0x26e/0x276
[ 954.674123] IN-SOFTIRQ-W at:
[ 954.674123] [<ffffffff8117f849>] __lock_acquire+0x899/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67e5c>] _raw_spin_lock_irqsave+0x7c/0xc0
[ 954.674123] [<ffffffff811377d2>] posix_timer_fn+0x32/0xd0
[ 954.674123] [<ffffffff8113df49>] __run_hrtimer+0x279/0x4d0
[ 954.674123] [<ffffffff8113eff9>] hrtimer_interrupt+0x109/0x210
[ 954.674123] [<ffffffff8113f13a>] __hrtimer_peek_ahead_timers+0x3a/0x50
[ 954.674123] [<ffffffff8113f191>] hrtimer_peek_ahead_timers+0x41/0xa0
[ 954.674123] [<ffffffff8113f227>] run_hrtimer_softirq+0x37/0x40
[ 954.674123] [<ffffffff81113897>] __do_softirq+0x1c7/0x440
[ 954.674123] [<ffffffff81113b48>] run_ksoftirqd+0x38/0xa0
[ 954.674123] [<ffffffff81144440>] smpboot_thread_fn+0x2b0/0x2e0
[ 954.674123] [<ffffffff81138b63>] kthread+0xe3/0xf0
[ 954.674123] [<ffffffff83a698bc>] ret_from_fork+0x7c/0xb0
[ 954.674123] INITIAL USE at:
[ 954.674123] [<ffffffff8117f997>] __lock_acquire+0x9e7/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67e5c>] _raw_spin_lock_irqsave+0x7c/0xc0
[ 954.674123] [<ffffffff811374a6>] __lock_timer+0xa6/0x1a0
[ 954.674123] [<ffffffff81137e37>] sys_timer_gettime+0x17/0x100
[ 954.674123] [<ffffffff83a69b98>] tracesys+0xe1/0xe6
[ 954.674123] }
[ 954.674123] ... key at: [<ffffffff85d6b940>] __key.30461+0x0/0x8
[ 954.674123] ... acquired at:
[ 954.674123] [<ffffffff8117d4ca>] check_irq_usage+0x6a/0xe0
[ 954.674123] [<ffffffff811804ba>] __lock_acquire+0x150a/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67f70>] _raw_spin_lock_bh+0x40/0x80
[ 954.674123] [<ffffffff8196409d>] yama_ptracer_del+0x1d/0xa0
[ 954.674123] [<ffffffff819644ec>] yama_task_free+0xc/0x10
[ 954.674123] [<ffffffff81923b41>] security_task_free+0x11/0x30
[ 954.674123] [<ffffffff81106ab8>] __put_task_struct+0x68/0x110
[ 954.674123] [<ffffffff8113b6b7>] posix_cpu_timer_del+0xa7/0xe0
[ 954.674123] [<ffffffff81138435>] exit_itimers+0x145/0x160
[ 954.674123] [<ffffffff8111055a>] do_exit+0x1aa/0xbd0
[ 954.674123] [<ffffffff81111044>] do_group_exit+0x84/0xd0
[ 954.674123] [<ffffffff811110a2>] sys_exit_group+0x12/0x20
[ 954.674123] [<ffffffff83a69b98>] tracesys+0xe1/0xe6
[ 954.674123]
[ 954.674123]
the dependencies between the lock to be acquired and HARDIRQ-irq-unsafe lock:
[ 954.674123] -> (ptracer_relations_lock){+.....} ops: 8538 {
[ 954.674123] HARDIRQ-ON-W at:
[ 954.674123] [<ffffffff8117f8df>] __lock_acquire+0x92f/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67f70>] _raw_spin_lock_bh+0x40/0x80
[ 954.674123] [<ffffffff8196409d>] yama_ptracer_del+0x1d/0xa0
[ 954.674123] [<ffffffff819644ec>] yama_task_free+0xc/0x10
[ 954.674123] [<ffffffff81923b41>] security_task_free+0x11/0x30
[ 954.674123] [<ffffffff81106ab8>] __put_task_struct+0x68/0x110
[ 954.674123] [<ffffffff8110e6b8>] delayed_put_task_struct+0x118/0x180
[ 954.674123] [<ffffffff811c9739>] rcu_do_batch.isra.14+0x5a9/0xab0
[ 954.674123] [<ffffffff811c9e5a>] rcu_cpu_kthread+0x21a/0x630
[ 954.674123] [<ffffffff81144440>] smpboot_thread_fn+0x2b0/0x2e0
[ 954.674123] [<ffffffff81138b63>] kthread+0xe3/0xf0
[ 954.674123] [<ffffffff83a698bc>] ret_from_fork+0x7c/0xb0
[ 954.674123] INITIAL USE at:
[ 954.674123] [<ffffffff8117f997>] __lock_acquire+0x9e7/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67f70>] _raw_spin_lock_bh+0x40/0x80
[ 954.674123] [<ffffffff8196409d>] yama_ptracer_del+0x1d/0xa0
[ 954.674123] [<ffffffff819644ec>] yama_task_free+0xc/0x10
[ 954.674123] [<ffffffff81923b41>] security_task_free+0x11/0x30
[ 954.674123] [<ffffffff81106ab8>] __put_task_struct+0x68/0x110
[ 954.674123] [<ffffffff8110e6b8>] delayed_put_task_struct+0x118/0x180
[ 954.674123] [<ffffffff811c9739>] rcu_do_batch.isra.14+0x5a9/0xab0
[ 954.674123] [<ffffffff811c9e5a>] rcu_cpu_kthread+0x21a/0x630
[ 954.674123] [<ffffffff81144440>] smpboot_thread_fn+0x2b0/0x2e0
[ 954.674123] [<ffffffff81138b63>] kthread+0xe3/0xf0
[ 954.674123] [<ffffffff83a698bc>] ret_from_fork+0x7c/0xb0
[ 954.674123] }
[ 954.674123] ... key at: [<ffffffff854ebcb8>] ptracer_relations_lock+0x18/0x50
[ 954.674123] ... acquired at:
[ 954.674123] [<ffffffff8117d4ca>] check_irq_usage+0x6a/0xe0
[ 954.674123] [<ffffffff811804ba>] __lock_acquire+0x150a/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff83a67f70>] _raw_spin_lock_bh+0x40/0x80
[ 954.674123] [<ffffffff8196409d>] yama_ptracer_del+0x1d/0xa0
[ 954.674123] [<ffffffff819644ec>] yama_task_free+0xc/0x10
[ 954.674123] [<ffffffff81923b41>] security_task_free+0x11/0x30
[ 954.674123] [<ffffffff81106ab8>] __put_task_struct+0x68/0x110
[ 954.674123] [<ffffffff8113b6b7>] posix_cpu_timer_del+0xa7/0xe0
[ 954.674123] [<ffffffff81138435>] exit_itimers+0x145/0x160
[ 954.674123] [<ffffffff8111055a>] do_exit+0x1aa/0xbd0
[ 954.674123] [<ffffffff81111044>] do_group_exit+0x84/0xd0
[ 954.674123] [<ffffffff811110a2>] sys_exit_group+0x12/0x20
[ 954.674123] [<ffffffff83a69b98>] tracesys+0xe1/0xe6
[ 954.674123]
[ 954.674123]
[ 954.674123] stack backtrace:
[ 954.674123] Pid: 8145, comm: trinity-child34 Tainted: G W 3.7.0-rc1-next-20121017-sasha-00002-g2353878-dirty #54
[ 954.674123] Call Trace:
[ 954.674123] [<ffffffff8117d43c>] check_usage+0x49c/0x4c0
[ 954.674123] [<ffffffff8117d4ca>] check_irq_usage+0x6a/0xe0
[ 954.674123] [<ffffffff811804ba>] __lock_acquire+0x150a/0x1ca0
[ 954.674123] [<ffffffff810a4e39>] ? pvclock_clocksource_read+0x69/0x100
[ 954.674123] [<ffffffff81180b00>] ? __lock_acquire+0x1b50/0x1ca0
[ 954.674123] [<ffffffff8118324a>] lock_acquire+0x1aa/0x240
[ 954.674123] [<ffffffff8196409d>] ? yama_ptracer_del+0x1d/0xa0
[ 954.674123] [<ffffffff81076bf5>] ? sched_clock+0x15/0x20
[ 954.674123] [<ffffffff83a67f70>] _raw_spin_lock_bh+0x40/0x80
[ 954.674123] [<ffffffff8196409d>] ? yama_ptracer_del+0x1d/0xa0
[ 954.674123] [<ffffffff8117b2e2>] ? get_lock_stats+0x22/0x70
[ 954.674123] [<ffffffff8196409d>] yama_ptracer_del+0x1d/0xa0
[ 954.674123] [<ffffffff819644ec>] yama_task_free+0xc/0x10
[ 954.674123] [<ffffffff81923b41>] security_task_free+0x11/0x30
[ 954.674123] [<ffffffff81106ab8>] __put_task_struct+0x68/0x110
[ 954.674123] [<ffffffff8113b6b7>] posix_cpu_timer_del+0xa7/0xe0
[ 954.674123] [<ffffffff81138435>] exit_itimers+0x145/0x160
[ 954.674123] [<ffffffff8111055a>] do_exit+0x1aa/0xbd0
[ 954.674123] [<ffffffff811cae05>] ? rcu_user_exit+0xc5/0xf0
[ 954.674123] [<ffffffff8117de7d>] ? trace_hardirqs_on+0xd/0x10
[ 954.674123] [<ffffffff81111044>] do_group_exit+0x84/0xd0
[ 954.674123] [<ffffffff811110a2>] sys_exit_group+0x12/0x20
[ 954.674123] [<ffffffff83a69b98>] tracesys+0xe1/0xe6


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