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SubjectRe: rcu,sched: spinlock recursion on 3.5-rc2
On Tue, 12 Jun 2012, Sasha Levin wrote:

> Hey all,
>
> I've got the following splat while fuzzing with trinity in a KVM tools guest on 3.5-rc2:
>
> [ 8110.274070] BUG: spinlock recursion on CPU#0, rcu_torture_rea/2658
> [ 8110.275014] lock: 0xffff88000d9d6140, .magic: dead4ead, .owner: rcu_torture_rea/2658, .owner_cpu: 0
> [ 8110.275014] Pid: 2658, comm: rcu_torture_rea Tainted: G W 3.5.0-rc2-sasha-00019-gbd68491 #376
> [ 8110.275014] Call Trace:
> [ 8110.275014] [<ffffffff8197de38>] spin_dump+0x78/0xc0
> [ 8110.275014] [<ffffffff8197deab>] spin_bug+0x2b/0x40
> [ 8110.275014] [<ffffffff8197dfee>] do_raw_spin_lock+0x4e/0x140
> [ 8110.275014] [<ffffffff837c0b2b>] _raw_spin_lock+0x5b/0x70
> [ 8110.275014] [<ffffffff8111d051>] ? rt_mutex_setprio+0x81/0x2c0
> [ 8110.275014] [<ffffffff8111d051>] rt_mutex_setprio+0x81/0x2c0
> [ 8110.275014] [<ffffffff81155160>] __rt_mutex_adjust_prio+0x20/0x30
> [ 8110.275014] [<ffffffff837c0164>] rt_mutex_slowunlock+0x104/0x130
> [ 8110.275014] [<ffffffff837c0199>] rt_mutex_unlock+0x9/0x10
> [ 8110.275014] [<ffffffff81193e30>] rcu_read_unlock_special+0x350/0x400
> [ 8110.275014] [<ffffffff8114841a>] ? get_lock_stats+0x2a/0x60
> [ 8110.275014] [<ffffffff811941aa>] rcu_preempt_note_context_switch+0x22a/0x300
> [ 8110.275014] [<ffffffff837bf8ca>] __schedule+0x76a/0x880
> [ 8110.275014] [<ffffffff837c1c74>] ? retint_restore_args+0x13/0x13
> [ 8110.275014] [<ffffffff8118dc20>] ? rcu_torture_read_unlock+0x40/0x60
> [ 8110.275014] [<ffffffff837bff64>] preempt_schedule_irq+0x94/0xd0
> [ 8110.275014] [<ffffffff837c1da6>] retint_kernel+0x26/0x30
> [ 8110.275014] [<ffffffff81193ae1>] ? rcu_read_unlock_special+0x1/0x400
> [ 8110.275014] [<ffffffff81193f2d>] ? __rcu_read_unlock+0x4d/0xa0
> [ 8110.275014] [<ffffffff8118dc3d>] rcu_torture_read_unlock+0x5d/0x60
> [ 8110.275014] [<ffffffff8118dedd>] rcu_torture_reader+0x29d/0x380
> [ 8110.275014] [<ffffffff8118ca50>] ? T.865+0x50/0x50
> [ 8110.275014] [<ffffffff8118dc40>] ? rcu_torture_read_unlock+0x60/0x60
> [ 8110.275014] [<ffffffff81106e32>] kthread+0xb2/0xc0
> [ 8110.275014] [<ffffffff837c39f4>] kernel_thread_helper+0x4/0x10
> [ 8110.275014] [<ffffffff837c1c74>] ? retint_restore_args+0x13/0x13
> [ 8110.275014] [<ffffffff81106d80>] ? __init_kthread_worker+0x70/0x70
> [ 8110.275014] [<ffffffff837c39f0>] ? gs_change+0x13/0x13

Ok, that's nasty.

The torture thread got preempted. rcu_preempt_note_context_switch()
tries to unlock the boosting rt mutex.

Though rcu_preempt_note_context_switch() is called with rq lock
held. So it's not a surprise that the code will dead lock.

My brain hurts already from looking, so Paul to the rescue!

Thanks,

tglx




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