Jens: can this be a plugging issue?

The following command seems to block for ever:
# mount /home

It is an ext3 fs on top of /dev/md0, RAID1.

The call trace is:

 mount         D 000000210a34f3b6  5488  5574   5555                     (NOTLB)
  ffff8100799718c8 0000000000000046 0000000000000000 0000000000000286
  0000000000000000 0000000000000286 ffff81007dc67220 0000000000000020
  0000000000000008 ffff810037c42040 ffffffff813a74e0 0000000000001441
 Call Trace:
  [<ffffffff81061b5a>] getnstimeofday+0x3a/0xa0
  [<ffffffff810699d8>] io_schedule+0x98/0xd0
  [<ffffffff810f1619>] sleep_on_buffer+0x9/0x10
  [<ffffffff81069c95>] __wait_on_bit+0x45/0x80
  [<ffffffff810f1610>] sleep_on_buffer+0x0/0x10
  [<ffffffff810f1610>] sleep_on_buffer+0x0/0x10
  [<ffffffff81069d48>] out_of_line_wait_on_bit+0x78/0x90
  [<ffffffff810a25f0>] wake_bit_function+0x0/0x40
  [<ffffffff8104f5e0>] __wait_on_buffer+0x20/0x30
  [<ffffffff8103ecbd>] sync_dirty_buffer+0xad/0xf0
  [<ffffffff8111957a>] ext3_commit_super+0x6a/0x80
  [<ffffffff81119ef6>] ext3_setup_super+0x106/0x1c0
  [<ffffffff8103f5de>] d_instantiate+0x9e/0xb0
  [<ffffffff8111bf94>] ext3_fill_super+0x12f4/0x1650
  [<ffffffff810de747>] get_sb_bdev+0x117/0x180
  [<ffffffff8111aca0>] ext3_fill_super+0x0/0x1650
  [<ffffffff81119363>] ext3_get_sb+0x13/0x20
  [<ffffffff810de150>] vfs_kern_mount+0xc0/0x160
  [<ffffffff810de25a>] do_kern_mount+0x4a/0x70
  [<ffffffff810e8fce>] do_mount+0x73e/0x7c0
  [<ffffffff8106c23b>] _read_unlock_irq+0x2b/0x40
  [<ffffffff8101c42f>] bad_range+0x1f/0x80
  [<ffffffff8100a4a7>] get_page_from_freelist+0x307/0x600
  [<ffffffff810240bb>] __up_read+0x8b/0xa0
  [<ffffffff8100f8f5>] __alloc_pages+0x75/0x320
  [<ffffffff81016a79>] alloc_pages_current+0xb9/0xd0
  [<ffffffff81051ad4>] sys_mount+0x94/0xf0
  [<ffffffff8106b8b1>] trace_hardirqs_on_thunk+0x35/0x37
  [<ffffffff8106511e>] system_call+0x7e/0x83
 

My precious data!
After that, the system just refuses to shutdown or sync:

 shutdown      D 0000004f59251224  4880  5622   5576                     (NOTLB)
  ffff8100796cfe78 0000000000000046 0000000000000000 ffffffff8104d0c2
  0000000000000000 0000000000000246 0000000000000000 0000000000000246
  0000000000000006 ffff810079082080 ffffffff813a74e0 000000000000545a
 Call Trace:
  [<ffffffff8104d0c2>] pagevec_lookup_tag+0x22/0x30
  [<ffffffff8106b775>] __down_read+0x95/0xb4
  [<ffffffff810a4da1>] down_read+0x41/0x50
  [<ffffffff810ee4f8>] __sync_inodes+0x78/0x120
  [<ffffffff810c57a0>] background_writeout+0x0/0xd0
  [<ffffffff810ee5c1>] sync_inodes+0x21/0x50
  [<ffffffff810f0efa>] do_sync+0x1a/0x60
  [<ffffffff810f0f4e>] sys_sync+0xe/0x20
  [<ffffffff8106511e>] system_call+0x7e/0x83
 
 sync          D 00000061fa86adc8  5680  5649   5624                     (NOTLB)
  ffff8100789abe78 0000000000000046 0000000000000000 ffffffff8104d0c2
  0000000000000000 0000000000000246 0000000000000000 0000000000000246
  0000000000000008 ffff81007842e0c0 ffffffff813a74e0 0000000000002b68
 Call Trace:
  [<ffffffff8104d0c2>] pagevec_lookup_tag+0x22/0x30
  [<ffffffff8106b775>] __down_read+0x95/0xb4
  [<ffffffff810a4da1>] down_read+0x41/0x50
  [<ffffffff810ee4f8>] __sync_inodes+0x78/0x120
  [<ffffffff810c57a0>] background_writeout+0x0/0xd0
  [<ffffffff810ee5c1>] sync_inodes+0x21/0x50
  [<ffffffff810f0efa>] do_sync+0x1a/0x60
  [<ffffffff810f0f4e>] sys_sync+0xe/0x20
  [<ffffffff8106511e>] system_call+0x7e/0x83
 
 
 Showing all locks held in the system:
 2 locks held by init/1:
  #0:  (tty_mutex){--..}, at: [<ffffffff8106a5e5>] mutex_lock+0x25/0x30
  #1:  (&sysfs_inode_imutex_key){--..}, at: [<ffffffff8106a5e5>] mutex_lock+0x25/0x30
 
Thanks,
Wu