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

[Jeff Layton <jlayton@redhat.com>]

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?

--- 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>