On 6/20/11 8:48 PM, Peter Zijlstra wrote:
Hi Pekka,
Thomas found a fun lockdep splat, see below. Basically call_rcu() can
end up in kmem_cache_alloc(), and call_rcu() is used under
l3->list_lock, causing the splat. Since the debug kmem_cache isn't
SLAB_DESTROY_BY_RCU this shouldn't ever actually recurse.
Now, since this particular kmem_cache is created with
SLAB_DEBUG_OBJECTS, we thought it might be easy enough to set a separate
lockdep class for its l3->list_lock's.
However I found that the existing lockdep annotation is for kmalloc only
-- don't custom kmem_caches use OFF_SLAB?
Looks like a bug. Custom caches can use OFF_SLAB too.
Anyway, I got lost in slab (again), but would it make sense to move all
lockdep fixups into kmem_list3_init() or thereabouts?
Yup.
---
=============================================
[ INFO: possible recursive locking detected ]
3.0.0-rc3+ #37
---------------------------------------------
udevd/124 is trying to acquire lock:
(&(&parent->list_lock)->rlock){......}, at: [<ffffffff81119619>] ____cache_alloc+0xc9/0x323
but task is already holding lock:
(&(&parent->list_lock)->rlock){......}, at: [<ffffffff8111844e>] __cache_free+0x325/0x3ea
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&(&parent->list_lock)->rlock);
lock(&(&parent->list_lock)->rlock);
*** DEADLOCK ***
May be due to missing lock nesting notation
2 locks held by udevd/124:
#0: (&(&(*({ do { const void *__vpp_verify = (typeof((&(slab_lock))))((void *)0); (void)__vpp_verify; } while (0); ({ unsigned long __ptr; __asm__ ("" : "=r"(__ptr) : "0"((typeof(*(&(slab_lock))) *)(&(slab_lock)))); (typeof((typeof(*(&(slab_lock))) *)(&(slab_lock)))) (__ptr + (((__per_cpu_offset[__cpu])))); }); })).lock)->rlock){..-...}, at: [<ffffffff811164cc>] __local_lock_irq+0x16/0x61
#1: (&(&parent->list_lock)->rlock){......}, at: [<ffffffff8111844e>] __cache_free+0x325/0x3ea
stack backtrace:
Pid: 124, comm: udevd Not tainted 3.0.0-rc3+ #37
Call Trace:
[<ffffffff81081e3d>] __lock_acquire+0x9ae/0xdc8
[<ffffffff8107f289>] ? look_up_lock_class+0x5f/0xbe
[<ffffffff810812e4>] ? mark_lock+0x2d/0x1d8
[<ffffffff81119619>] ? ____cache_alloc+0xc9/0x323
[<ffffffff81082774>] lock_acquire+0x103/0x12e
[<ffffffff81119619>] ? ____cache_alloc+0xc9/0x323
[<ffffffff8107f6b9>] ? register_lock_class+0x1e/0x2ca
[<ffffffff81247054>] ? __debug_object_init+0x43/0x2e7
[<ffffffff814a7730>] _raw_spin_lock+0x3b/0x4a
[<ffffffff81119619>] ? ____cache_alloc+0xc9/0x323
[<ffffffff81119619>] ____cache_alloc+0xc9/0x323
[<ffffffff8107f6b9>] ? register_lock_class+0x1e/0x2ca
[<ffffffff81247054>] ? __debug_object_init+0x43/0x2e7
[<ffffffff8111b0d5>] kmem_cache_alloc+0xc5/0x1fb
[<ffffffff81247054>] __debug_object_init+0x43/0x2e7
[<ffffffff8124735f>] ? debug_object_activate+0x38/0xdc
[<ffffffff810812e4>] ? mark_lock+0x2d/0x1d8
[<ffffffff8124730c>] debug_object_init+0x14/0x16
[<ffffffff8106bd26>] rcuhead_fixup_activate+0x2b/0xbc
[<ffffffff81246d6f>] debug_object_fixup+0x1e/0x2b
[<ffffffff812473f6>] debug_object_activate+0xcf/0xdc
[<ffffffff81118b93>] ? kmem_cache_shrink+0x68/0x68
[<ffffffff810b1fc0>] __call_rcu+0x4f/0x19e
[<ffffffff810b2124>] call_rcu+0x15/0x17
[<ffffffff81117c4a>] slab_destroy+0x11f/0x157
[<ffffffff81117dd4>] free_block+0x152/0x18d
[<ffffffff81118497>] __cache_free+0x36e/0x3ea
[<ffffffff81103b3b>] ? anon_vma_free+0x3d/0x41
[<ffffffff811164cc>] ? __local_lock_irq+0x16/0x61
[<ffffffff81117aad>] kmem_cache_free+0xa1/0x11f
[<ffffffff81103b3b>] anon_vma_free+0x3d/0x41
[<ffffffff81104a77>] __put_anon_vma+0x38/0x3d
[<ffffffff81104aa5>] put_anon_vma+0x29/0x2d
[<ffffffff81104b7e>] unlink_anon_vmas+0x72/0xa5
[<ffffffff810faa5b>] free_pgtables+0x6c/0xcb
[<ffffffff81100c96>] exit_mmap+0xc0/0xf7
[<ffffffff8104de1d>] mmput+0x60/0xd3
[<ffffffff81054112>] exit_mm+0x141/0x14e
[<ffffffff814a7d75>] ? _raw_spin_unlock_irq+0x54/0x61
[<ffffffff8105436a>] do_exit+0x24b/0x74f
[<ffffffff811289ae>] ? fput+0x1d4/0x1e3
[<ffffffff8107f539>] ? trace_hardirqs_off_caller+0x33/0x90
[<ffffffff814a847d>] ? retint_swapgs+0x13/0x1b
[<ffffffff81054ae2>] do_group_exit+0x82/0xad
[<ffffffff81054b24>] sys_exit_group+0x17/0x1b
[<ffffffff814ae182>] system_call_fastpath+0x16/0x1b
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