Just got this with CONFIG_SLAB:

=============================================
[ INFO: possible recursive locking detected ]
2.6.33-rc1-dirty #23
---------------------------------------------
events/5/20 is trying to acquire lock:
 (&(&parent->list_lock)->rlock){..-...}, at: [<00000000000ee898>] cache_flusharray+0x3c/0x12c

but task is already holding lock:
 (&(&parent->list_lock)->rlock){..-...}, at: [<00000000000eee52>] drain_array+0x52/0x100

other info that might help us debug this:
4 locks held by events/5/20:
 #0:  (events){+.+.+.}, at: [<000000000006cbec>] worker_thread+0x1ec/0x33c
 #1:  ((&(reap_work)->work)){+.+...}, at: [<000000000006cbec>] worker_thread+0x1ec/0x33c
 #2:  (cache_chain_mutex){+.+.+.}, at: [<00000000000ef03a>] cache_reap+0x32/0x164
 #3:  (&(&parent->list_lock)->rlock){..-...}, at: [<00000000000eee52>] drain_array+0x52/0x100

stack backtrace:
CPU: 5 Not tainted 2.6.33-rc1-dirty #23
Process events/5 (pid: 20, task: 000000003fa48a38, ksp: 000000003fa4fc60)
000000003fa4f9b0 000000003fa4f930 0000000000000002 0000000000000000 
       000000003fa4f9d0 000000003fa4f948 000000003fa4f948 00000000003dce2a 
       0000000000000000 0000000000000000 000000003fa49190 0000000000827108 
       000000000000000d 000000000000000c 000000003fa4f998 0000000000000000 
       0000000000000000 00000000000174fa 000000003fa4f930 000000003fa4f970 
Call Trace:
([<0000000000017402>] show_trace+0xee/0x144)
 [<0000000000088f88>] validate_chain+0xa2c/0x1100
 [<0000000000089b70>] __lock_acquire+0x514/0xc4c
 [<000000000008a354>] lock_acquire+0xac/0xd4
 [<00000000003e0c68>] _raw_spin_lock+0x58/0x94
 [<00000000000ee898>] cache_flusharray+0x3c/0x12c
 [<00000000000eebd8>] kmem_cache_free+0xd4/0xf8
 [<00000000000eeda4>] free_block+0x11c/0x178
 [<00000000000eee92>] drain_array+0x92/0x100
 [<00000000000ef0fe>] cache_reap+0xf6/0x164
 [<000000000006cc6e>] worker_thread+0x26e/0x33c
 [<0000000000072d14>] kthread+0xa0/0xa8
 [<000000000001c10a>] kernel_thread_starter+0x6/0xc
 [<000000000001c104>] kernel_thread_starter+0x0/0xc
INFO: lockdep is turned off.

config attached.