lockdep recursive locking detected (rcu_kthread / __cache_free)

From: Sitsofe Wheeler
Date: Mon Oct 03 2011 - 13:53:40 EST


While running 3.1.0-rc8 the following lockdep warning (seemingly related
to RCU) was printed as the kernel was starting.

udev: starting version 151
udevd (263): /proc/263/oom_adj is deprecated, please use /proc/263/oom_score_adj instead.

[ INFO: possible recursive locking detected ]
3.1.0-rc8-dirty #508
rcu_kthread/6 is trying to acquire lock:
(&(&parent->list_lock)->rlock){..-...}, at: [<b016fe11>] __cache_free+0x2dd/0x382

but task is already holding lock:
(&(&parent->list_lock)->rlock){..-...}, at: [<b016fe11>] __cache_free+0x2dd/0x382

other info that might help us debug this:
Possible unsafe locking scenario:


*** DEADLOCK ***

May be due to missing lock nesting notation

1 lock held by rcu_kthread/6:
#0: (&(&parent->list_lock)->rlock){..-...}, at: [<b016fe11>] __cache_free+0x2dd/0x382

stack backtrace:
Pid: 6, comm: rcu_kthread Not tainted 3.1.0-rc8-dirty #508
Call Trace:
[<b0144466>] __lock_acquire+0xb90/0xc0e
[<b044c0c2>] ? _raw_spin_unlock_irqrestore+0x2f/0x46
[<b0223ebc>] ? debug_object_active_state+0x94/0xbc
[<b01315af>] ? rcuhead_fixup_activate+0x26/0x4c
[<b01448be>] lock_acquire+0x5b/0x72
[<b016fe11>] ? __cache_free+0x2dd/0x382
[<b044bb22>] _raw_spin_lock+0x25/0x34
[<b016fe11>] ? __cache_free+0x2dd/0x382
[<b016fe11>] __cache_free+0x2dd/0x382
[<b016ff5c>] kmem_cache_free+0x3e/0x5b
[<b0170097>] slab_destroy+0x11e/0x126
[<b0170184>] free_block+0xe5/0x112
[<b016fe54>] __cache_free+0x320/0x382
[<b01759a1>] ? file_free_rcu+0x32/0x39
[<b016ff5c>] kmem_cache_free+0x3e/0x5b
[<b01759a1>] file_free_rcu+0x32/0x39
[<b014ca68>] rcu_process_callbacks+0x95/0xa8
[<b014cb34>] rcu_kthread+0xb9/0xd2
[<b013356c>] ? wake_up_bit+0x1b/0x1b
[<b014ca7b>] ? rcu_process_callbacks+0xa8/0xa8
[<b0133305>] kthread+0x6c/0x71
[<b0133299>] ? __init_kthread_worker+0x42/0x42
[<b044ce02>] kernel_thread_helper+0x6/0xd

Sitsofe | http://sucs.org/~sits/
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