BUG: task blocked on waiter in xfs_trans_dqlockedjoin()

[Alex Elder <elder@dreamhost.com>]

I am getting the following warning while running xfstests.  I haven't
started looking at it closely yet, but I wanted to report it so others
could have a look.  The XFS code in use was at commit c922bbc819,
with ad637a10f4 cherry-picked on top of it.  The tests all passed,
so now I'm going to have to narrow down which test produces the failure
(it was not near the first, nor the last test...).

Here is the source of the warning:
         DEBUG_LOCKS_WARN_ON(ti->task->blocked_on != waiter);

In this function:
void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
                          struct thread_info *ti)
{
         DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
         DEBUG_LOCKS_WARN_ON(waiter->task != ti->task);
         DEBUG_LOCKS_WARN_ON(ti->task->blocked_on != waiter);
         ti->task->blocked_on = NULL;

         list_del_init(&waiter->list);
         waiter->task = NULL;
}

called (eventually) via xfs_dqlock2() in this function:

STATIC void
xfs_trans_dqlockedjoin(
         xfs_trans_t     *tp,
         xfs_dqtrx_t     *q)
{
         ASSERT(q[0].qt_dquot != NULL);
         if (q[1].qt_dquot == NULL) {
                 xfs_dqlock(q[0].qt_dquot);
                 xfs_trans_dqjoin(tp, q[0].qt_dquot);
         } else {
                 ASSERT(XFS_QM_TRANS_MAXDQS == 2);
                 xfs_dqlock2(q[0].qt_dquot, q[1].qt_dquot);
                 xfs_trans_dqjoin(tp, q[0].qt_dquot);
                 xfs_trans_dqjoin(tp, q[1].qt_dquot);
         }
}


					-Alex

------------[ cut here ]------------
WARNING: at 
/srv/autobuild-ceph/gitbuilder.git/build/kernel/mutex-debug.c:65 
mutex_remove_waiter+0x93/0x130()
Hardware name: PowerEdge R410
Modules linked in: rbd libceph aesni_intel cryptd aes_x86_64 aes_generic 
ufs qnx4 hfsplus hfs minix ntfs vfat msdos fat jfs xfs exportfs reiserfs 
ipmi_devintf ipmi_si ipmi_msghandler i7core_edac edac_core joydev hed 
serio_raw dcdbas lp parport usbhid hid mptsas ixgbe mptscsih mptbase dca 
mdio scsi_transport_sas bnx2 btrfs zlib_deflate crc32c libcrc32c [last 
unloaded: libceph]
Pid: 5947, comm: kworker/0:4 Not tainted 3.3.0-ceph-00067-gafede88 #1
Call Trace:
  [<ffffffff8104e42f>] warn_slowpath_common+0x7f/0xc0
  [<ffffffff8104e48a>] warn_slowpath_null+0x1a/0x20
  [<ffffffff810a59f3>] mutex_remove_waiter+0x93/0x130
  [<ffffffff8161309c>] __mutex_lock_common+0x24c/0x3d0
  [<ffffffffa0293a4f>] ? xfs_trans_dqlockedjoin+0x5f/0x70 [xfs]
  [<ffffffffa0293a4f>] ? xfs_trans_dqlockedjoin+0x5f/0x70 [xfs]
  [<ffffffff81613347>] mutex_lock_nested+0x37/0x50
  [<ffffffffa0293a4f>] xfs_trans_dqlockedjoin+0x5f/0x70 [xfs]
  [<ffffffffa0293aa5>] xfs_trans_apply_dquot_deltas+0x45/0x290 [xfs]
  [<ffffffffa0287257>] xfs_trans_commit+0x67/0x270 [xfs]
  [<ffffffffa023e52b>] xfs_iomap_write_allocate+0x16b/0x380 [xfs]
  [<ffffffffa0232575>] xfs_map_blocks+0x165/0x240 [xfs]
  [<ffffffffa02327ef>] xfs_vm_writepage+0x19f/0x500 [xfs]
  [<ffffffff8112990a>] __writepage+0x1a/0x50
  [<ffffffff8112b66e>] write_cache_pages+0x24e/0x4e0
  [<ffffffff8130e01f>] ? cfq_dispatch_requests+0x18f/0xc10
  [<ffffffff811298f0>] ? set_page_dirty+0x70/0x70
  [<ffffffff8112b954>] generic_writepages+0x54/0x80
  [<ffffffffa02311bc>] xfs_vm_writepages+0x5c/0x80 [xfs]
  [<ffffffff8112b9a4>] do_writepages+0x24/0x40
  [<ffffffff81120b4b>] __filemap_fdatawrite_range+0x5b/0x60
  [<ffffffff81120e23>] filemap_fdatawrite_range+0x13/0x20
  [<ffffffffa023a818>] xfs_flush_pages+0x78/0xc0 [xfs]
  [<ffffffffa0245416>] xfs_sync_inode_data+0x86/0xb0 [xfs]
  [<ffffffffa0245a7e>] xfs_inode_ag_walk+0x20e/0x370 [xfs]
  [<ffffffffa0245b5b>] ? xfs_inode_ag_walk+0x2eb/0x370 [xfs]
  [<ffffffffa0245390>] ? xfs_sync_worker+0x90/0x90 [xfs]
  [<ffffffffa0245390>] ? xfs_sync_worker+0x90/0x90 [xfs]
  [<ffffffffa0245c25>] xfs_inode_ag_iterator+0x45/0xa0 [xfs]
  [<ffffffffa0245ca9>] xfs_sync_data+0x29/0x50 [xfs]
  [<ffffffffa0245cf2>] xfs_flush_worker+0x22/0x40 [xfs]
  [<ffffffff8106b256>] process_one_work+0x1a6/0x520
  [<ffffffff8106b1e7>] ? process_one_work+0x137/0x520
  [<ffffffffa0245cd0>] ? xfs_sync_data+0x50/0x50 [xfs]
  [<ffffffff8106d71e>] worker_thread+0x2fe/0x400
  [<ffffffff8106d420>] ? manage_workers+0x210/0x210
  [<ffffffff8107280e>] kthread+0xbe/0xd0
  [<ffffffff8161f5f4>] kernel_thread_helper+0x4/0x10
  [<ffffffff81616134>] ? retint_restore_args+0x13/0x13
  [<ffffffff81072750>] ? __init_kthread_worker+0x70/0x70
  [<ffffffff8161f5f0>] ? gs_change+0x13/0x13
---[ end trace d27597ce9ccb8690 ]---

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