Re: WARNING: at lib/debugobjects.c:262 debug_print_object+0x8c/0xb0()

[Boaz Harrosh <bharrosh@panasas.com>]

On 01/24/2012 09:45 AM, Stanislaw Gruszka wrote:
> On Mon, Jan 23, 2012 at 10:23:11AM -0500, Jeff Layton wrote:
>> On Sun, 22 Jan 2012 00:46:14 -0800
>> Stephen Boyd <sboyd@codeaurora.org> wrote:
>>
>>> On 1/20/2012 10:56 AM, Jeff Layton wrote:
>>>> What I'm finding though is that if I stop and start nfsd multiple
>>>> times, then I eventually get a warning like this on start:
>>>>
>>>> [ 5157.128514] WARNING: at lib/debugobjects.c:262 debug_print_object+0x8c/0xb0()
>>>> [ 5157.128742] Hardware name: Bochs
>>>> [ 5157.128742] ODEBUG: activate not available (active state 0) object type: timer_list hint: stub_timer+0x0/0x20
>>>> [ 5157.128742] Modules linked in: nfsd(O) nfs_acl auth_rpcgss lockd sunrpc floppy virtio_net i2c_piix4 i2c_core virtio_balloon joydev pcspkr virtio_blk [last unloaded: nfsd]
>>>> [ 5157.128742] Pid: 1312, comm: rpc.nfsd Tainted: G        W  O 3.3.0-rc1+ #1
>>>> [ 5157.128742] Call Trace:
>>>> [ 5157.128742]  [<ffffffff8106135f>] warn_slowpath_common+0x7f/0xc0
>>>> [ 5157.128742]  [<ffffffff81061456>] warn_slowpath_fmt+0x46/0x50
>>>> [ 5157.128742]  [<ffffffff8132ba2c>] debug_print_object+0x8c/0xb0
>>>> [ 5157.128742]  [<ffffffff81070db0>] ? timer_debug_hint+0x10/0x10
>>>> [ 5157.128742]  [<ffffffff8132c02b>] debug_object_activate+0xfb/0x190
>>>> [ 5157.128742]  [<ffffffff81072728>] ? lock_timer_base.isra.24+0x38/0x70
>>>> [ 5157.128742]  [<ffffffff81074676>] mod_timer+0xf6/0x450
>>>> [ 5157.128742]  [<ffffffff810749e8>] add_timer+0x18/0x20
>>>> [ 5157.128742]  [<ffffffff8108168e>] queue_delayed_work_on+0xbe/0x140
>>>> [ 5157.128742]  [<ffffffff81084441>] queue_delayed_work+0x21/0x40
>>>> [ 5157.128742]  [<ffffffffa006e568>] rpc_queue_upcall+0xe8/0x100 [sunrpc]
>>>> [ 5157.128742]  [<ffffffffa012a121>] __cld_pipe_upcall+0x61/0xc0 [nfsd]
>>>> [ 5157.128742]  [<ffffffffa012ad98>] nfsd4_cld_init+0x48/0x140 [nfsd]
>>>> [ 5157.128742]  [<ffffffffa012b22a>] nfsd4_client_tracking_init+0x2a/0xc0 [nfsd]
>>>> [ 5157.128742]  [<ffffffff8169797e>] ? mutex_unlock+0xe/0x10
>>>> [ 5157.128742]  [<ffffffffa01266fa>] nfs4_state_start+0x1a/0x100 [nfsd]
>>>> [ 5157.128742]  [<ffffffffa01028c5>] nfsd_svc+0x135/0x200 [nfsd]
>>>> [ 5157.128742]  [<ffffffffa0103df0>] ? write_maxblksize+0x130/0x130 [nfsd]
>>>> [ 5157.128742]  [<ffffffffa0103e6d>] write_threads+0x7d/0xd0 [nfsd]
>>>> [ 5157.128742]  [<ffffffff811dd16a>] ? simple_transaction_get+0xca/0xe0
>>>> [ 5157.128742]  [<ffffffffa0102ee7>] nfsctl_transaction_write+0x57/0x90 [nfsd]
>>>> [ 5157.128742]  [<ffffffff811b4c9f>] vfs_write+0xaf/0x190
>>>> [ 5157.128742]  [<ffffffff811b4fdd>] sys_write+0x4d/0x90
>>>> [ 5157.128742]  [<ffffffff816a3469>] system_call_fastpath+0x16/0x1b
>>>
>>> This one is telling you that the timer you're about to run hasn't been 
>>> registered with debug_objects. Most likely the work item hasn't been 
>>> initialized properly and so it hasn't had INIT_DELAYED_WORK() called on it.
>>>
>>>>
>>>> ...or this on stop:
>>>>
>>>> [ 5200.804410] WARNING: at lib/debugobjects.c:262 debug_print_object+0x8c/0xb0()
>>>> [ 5200.808205] Hardware name: Bochs
>>>> [ 5200.810121] ODEBUG: assert_init not available (active state 0) object type: timer_list hint: stub_timer+0x0/0x20
>>>> [ 5200.812734] Modules linked in: nfsd(O) nfs_acl auth_rpcgss lockd sunrpc floppy virtio_net i2c_piix4 i2c_core virtio_balloon joydev pcspkr virtio_blk [last unloaded: nfsd]
>>>> [ 5200.821596] Pid: 1394, comm: nfsd Tainted: G        W  O 3.3.0-rc1+ #1
>>>> [ 5200.822409] Call Trace:
>>>> [ 5200.822726]  [<ffffffff8106135f>] warn_slowpath_common+0x7f/0xc0
>>>> [ 5200.823509]  [<ffffffff81061456>] warn_slowpath_fmt+0x46/0x50
>>>> [ 5200.824243]  [<ffffffff8132ba2c>] debug_print_object+0x8c/0xb0
>>>> [ 5200.824935]  [<ffffffff81070db0>] ? timer_debug_hint+0x10/0x10
>>>> [ 5200.825665]  [<ffffffff8132c543>] debug_object_assert_init+0xe3/0x120
>>>> [ 5200.826474]  [<ffffffff810737b4>] del_timer+0x24/0x1b0
>>>> [ 5200.827129]  [<ffffffff81085314>] __cancel_work_timer+0x34/0x140
>>>> [ 5200.827829]  [<ffffffff81085432>] cancel_delayed_work_sync+0x12/0x20
>>>> [ 5200.832905]  [<ffffffffa006e430>] rpc_unlink+0x1e0/0x230 [sunrpc]
>>>> [ 5200.833716]  [<ffffffffa012a195>] nfsd4_remove_cld_pipe+0x15/0x40 [nfsd]
>>>> [ 5200.834558]  [<ffffffffa012b2e0>] nfsd4_client_tracking_exit+0x20/0x30 [nfsd]
>>>> [ 5200.835434]  [<ffffffffa0126984>] nfs4_state_shutdown+0x1a4/0x1c0 [nfsd]
>>>> [ 5200.836271]  [<ffffffffa010219a>] nfsd_last_thread+0x2a/0x60 [nfsd]
>>>> [ 5200.837045]  [<ffffffffa005f66c>] svc_destroy+0x5c/0x140 [sunrpc]
>>>> [ 5200.837778]  [<ffffffffa005f9f6>] svc_exit_thread+0xa6/0xb0 [sunrpc]
>>>> [ 5200.838545]  [<ffffffffa0102123>] nfsd+0x123/0x170 [nfsd]
>>>> [ 5200.839221]  [<ffffffffa0102000>] ? 0xffffffffa0101fff
>>>> [ 5200.839820]  [<ffffffff8108a747>] kthread+0xb7/0xc0
>>>> [ 5200.840431]  [<ffffffff816a48b4>] kernel_thread_helper+0x4/0x10
>>>> [ 5200.850883]  [<ffffffff8169acf4>] ? retint_restore_args+0x13/0x13
>>>> [ 5200.851654]  [<ffffffff8108a690>] ? kthread_worker_fn+0x1a0/0x1a0
>>>> [ 5200.852418]  [<ffffffff816a48b0>] ? gs_change+0x13/0x13
>>>
>>> This is similar. Now you're deleting a timer that debug_objects doesn't 
>>> know about.
>>>
>>>>
>>>> The problem is that even after staring at this code for a while, I'm
>>>> still clueless as to what this is telling me. It doesn't happen every
>>>> time either, so maybe there's a race of some sort involved.
>>>>
>>>> It's possible that my patch is broken and doing something wrong, but
>>>> I'm starting not to think so. I'm not really using timers directly --
>>>> I'm using rpc_pipefs, which queues a delayed job to a workqueue, and
>>>> that is manipulating the timer. The delayed_work (and hence the timer)
>>>> are part of an rpc_inode.
>>>>
>>>> Can anyone shed a little light on what this is complaining about?
>>>>
>>>
>>> Do you have workqueue debugging enabled too (DEBUG_OBJECTS_WORK)? I 
>>> would hope that work item debugging would say the same things and then 
>>> we would know that the work item itself wasn't initialized properly.
>>
>> (adding linux-nfs to cc list...)
>>
>> Ok, I think I sort of see what's happening, but I'm not sure if it's a
>> bug in the debug objects code or something else. To answer the question
>> that I didn't before, the kernels I've been testing have this set:
>>
>>     CONFIG_DEBUG_OBJECTS_WORK=y
>>
>> ...so workqueue debugging is on but I haven't seen any messages that
>> come from it AFAICT. The rpc_inode objects have their delayed_work
>> fields initialized via a slab "constructor". Here's the rpc_inode_cache
>> creation call:
>>
>>         rpc_inode_cachep = kmem_cache_create("rpc_inode_cache",
>>                                 sizeof(struct rpc_inode),
>>                                 0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT|
>>                                                 SLAB_MEM_SPREAD),
>>                                 init_once);
>>
>> ...and the init_once() routine does this:
>>
>>         INIT_DELAYED_WORK(&rpci->queue_timeout,
>>                             rpc_timeout_upcall_queue);
>>
>> On the first use of an rpc_inode object, everything works fine. I think
>> the problem comes in when rpc_inode objects get recycled without the
>> INIT_DELAYED_WORK() getting called on it again.
>>
>> Before the object is freed it gets cancel_delayed_work_sync() called on
>> it, but that's apparently not enough to convince the debugobjects code
>> that it's already correctly initialized. As a Q&D check, the following
>> patch seems to stop the warnings. Is there some better way to do this
>> that doesn't require the reinitialization of the delayed work on each
>> inode allocation?
> 
> If this is debug objects false positive, it should be rather fixed in
> debug object code itself, not workaround in nfs code, but I do not have
> any idea how to do this.
> 
> Stanislaw
>  

I don't think so. Look at what INIT_DELAYED_WORK does.
   INIT_WORK - Set some start values, register with the objects-debugger if on.
   init_timer - 

I'd imagine that cancel_delayed_work_sync() would: 1st cancel some of those
registrations, specifically with the objects-debugger. 2nd will leave some
state undefined as left from the last round.

I think this patch is cardinal and you might have found a potential bug.

Also the cost of INIT_DELAYED_WORK is marginal compare to the extra safety.

Recomended-by: Boaz Harrosh <bharrosh@panasas.com>

>> --- a/net/sunrpc/rpc_pipe.c
>> +++ b/net/sunrpc/rpc_pipe.c
>> @@ -178,6 +178,8 @@ rpc_alloc_inode(struct super_block *sb)
>>         rpci = (struct rpc_inode *)kmem_cache_alloc(rpc_inode_cachep, GFP_KERNEL);
>>         if (!rpci)
>>                 return NULL;
>> +
>> +       INIT_DELAYED_WORK(&rpci->queue_timeout, rpc_timeout_upcall_queue);
>>         return &rpci->vfs_inode;
>>  }
>>
>> -- 
>> Jeff Layton <jlayton@redhat.com>
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