2.6.39-rc7-mmotm0512 lockdep splat in scheduler code

[Valdis . Kletnieks]

Sorry if this was reported already but I missed it on the lkml firehose..

Seen this morning at boot while configuring the sound card. Semi-reproducible,
as it's tripped 3 times in the last 5 boots of this kernel. However, it hadn't
tripped once in the previous 15 boots of that same kernel (odd, as it's same
kernel binary and same initrd, and we're still on the initrd at this point). Not sure
what changed to make it start happening.

(/proc/interrupts lists:  48:      67445      66819   PCI-MSI-edge      hda_intel)

[    2.511386] HDA Intel 0000:00:1b.0: setting latency timer to 64
[    2.523230] 
[    2.523231] ===================================================
[    2.523234] [ INFO: suspicious rcu_dereference_check() usage. ]
[    2.523236] ---------------------------------------------------
[    2.523238] kernel/sched_rt.c:1244 invoked rcu_dereference_check() without protection!
[    2.523241] 
[    2.523241] other info that might help us debug this:
[    2.523242] 
[    2.523244] 
[    2.523245] rcu_scheduler_active = 1, debug_locks = 1
[    2.523247] 1 lock held by irq/48-hda_inte/85:
[    2.523249]  #0:  (&rq->lock){-.-.-.}, at: [<ffffffff8102adc9>] post_schedule.part.20+0xf/0x45
[    2.523259] 
[    2.523260] stack backtrace:
[    2.523263] Pid: 85, comm: irq/48-hda_inte Not tainted 2.6.39-rc7-mmotm0512 #2
[    2.523265] Call Trace:
[    2.523271]  [<ffffffff81066d8e>] lockdep_rcu_dereference+0x9a/0xa2
[    2.523275]  [<ffffffff8102c45e>] find_lowest_rq+0xf9/0x174
[    2.523279]  [<ffffffff8102d167>] find_lock_lowest_rq+0x2c/0xfe
[    2.523284]  [<ffffffff81032485>] push_rt_task.part.60+0xac/0x156
[    2.523288]  [<ffffffff81032633>] post_schedule_rt+0x1a/0x23
[    2.523291]  [<ffffffff8102ade5>] post_schedule.part.20+0x2b/0x45
[    2.523296]  [<ffffffff8156a651>] schedule+0x6f2/0x738
[    2.523301]  [<ffffffff8108c446>] ? irq_thread_fn+0x29/0x29
[    2.523305]  [<ffffffff8108c3df>] irq_thread+0x173/0x1b1
[    2.523309]  [<ffffffff8108c26c>] ? irq_finalize_oneshot+0xc9/0xc9
[    2.523314]  [<ffffffff81054e4e>] kthread+0x7f/0x87
[    2.523318]  [<ffffffff81573e54>] kernel_thread_helper+0x4/0x10
[    2.523322]  [<ffffffff8156d044>] ? retint_restore_args+0xe/0xe
[    2.523326]  [<ffffffff81054dcf>] ? __init_kthread_worker+0x55/0x55
[    2.523330]  [<ffffffff81573e50>] ? gs_change+0xb/0xb
[    2.523409] 
[    2.523409] ===================================================
[    2.523412] [ INFO: suspicious rcu_dereference_check() usage. ]
[    2.523414] ---------------------------------------------------
[    2.523416] kernel/sched.c:619 invoked rcu_dereference_check() without protection!
[    2.523418] 
[    2.523419] other info that might help us debug this:
[    2.523420] 
[    2.523422] 
[    2.523422] rcu_scheduler_active = 1, debug_locks = 1
[    2.523425] 2 locks held by irq/48-hda_inte/85:
[    2.523427]  #0:  (&rq->lock){-.-.-.}, at: [<ffffffff8102d0ca>] double_rq_lock+0x62/0x77
[    2.523434]  #1:  (&rq->lock/1){..-...}, at: [<ffffffff8102d0d7>] double_rq_lock+0x6f/0x77
[    2.523441] 
[    2.523442] stack backtrace:
[    2.523444] Pid: 85, comm: irq/48-hda_inte Not tainted 2.6.39-rc7-mmotm0512 #2
[    2.523446] Call Trace:
[    2.523450]  [<ffffffff81066d8e>] lockdep_rcu_dereference+0x9a/0xa2
[    2.523454]  [<ffffffff8102aecf>] task_group+0x7a/0xb9
[    2.523458]  [<ffffffff8102af20>] set_task_rq+0x12/0x6b
[    2.523462]  [<ffffffff810320d3>] set_task_cpu+0x8b/0xe8
[    2.523466]  [<ffffffff8121c985>] ? plist_check_head+0x120/0x125
[    2.523470]  [<ffffffff8121cb1b>] ? plist_del+0x70/0x79
[    2.523474]  [<ffffffff8102cd87>] ? dequeue_task_rt+0x33/0x38
[    2.523477]  [<ffffffff8102c9cd>] ? dequeue_task+0x9b/0xa7
[    2.523482]  [<ffffffff810324f5>] push_rt_task.part.60+0x11c/0x156
[    2.523486]  [<ffffffff81032633>] post_schedule_rt+0x1a/0x23
[    2.523489]  [<ffffffff8102ade5>] post_schedule.part.20+0x2b/0x45
[    2.523494]  [<ffffffff8156a651>] schedule+0x6f2/0x738
[    2.523497]  [<ffffffff8108c446>] ? irq_thread_fn+0x29/0x29
[    2.523501]  [<ffffffff8108c3df>] irq_thread+0x173/0x1b1
[    2.523505]  [<ffffffff8108c26c>] ? irq_finalize_oneshot+0xc9/0xc9
[    2.523509]  [<ffffffff81054e4e>] kthread+0x7f/0x87
[    2.523513]  [<ffffffff81573e54>] kernel_thread_helper+0x4/0x10
[    2.523517]  [<ffffffff8156d044>] ? retint_restore_args+0xe/0xe
[    2.523521]  [<ffffffff81054dcf>] ? __init_kthread_worker+0x55/0x55
[    2.523524]  [<ffffffff81573e50>] ? gs_change+0xb/0xb
[    2.548750] input: HDA Intel Mic at Sep Left Jack as /devices/pci0000:00/0000:00:1b.0/sound/card0/input6

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