Task blocked for more than 120 seconds

[Samuel Tardieu <sam@rfc1149.net>]

On my laptop, doing heavy C++ compilations in parallel with -j3 (this
is a dual core) often generates the following trace:

INFO: task g++:25119 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
g++           D c03916c0     0 25119  25118
       ecfef200 00200086 c038ef18 c03916c0 c03916c0 f77b2230 f77b2378 c17fa6c0 
       00000000 f89817bc f7486280 000000ff f7a1eb20 00000000 00000000 00000000 
       c17fa6c0 00000000 d1401e9c c17f0408 c02a2aa1 d1401e94 c0147100 c02a2c93 
Call Trace:
 [<f89817bc>] dm_table_unplug_all+0x1e/0x2e [dm_mod]
 [<c02a2aa1>] io_schedule+0x1b/0x24
 [<c0147100>] sync_page+0x33/0x36
 [<c02a2c93>] __wait_on_bit+0x33/0x58
 [<c01470cd>] sync_page+0x0/0x36
 [<c01472fd>] wait_on_page_bit+0x59/0x60
 [<c012cf7b>] wake_bit_function+0x0/0x3c
 [<c014e20d>] truncate_inode_pages_range+0x238/0x29f
 [<c014e27d>] truncate_inode_pages+0x9/0xc
 [<f8c67187>] ext2_delete_inode+0x12/0x6e [ext2]
 [<f8c67175>] ext2_delete_inode+0x0/0x6e [ext2]
 [<c0170ea5>] generic_delete_inode+0x8f/0xf3
 [<c0170819>] iput+0x60/0x62
 [<c0169aa5>] do_unlinkat+0xb7/0xf9
 [<c0113a3e>] do_page_fault+0x1fa/0x4dc
 [<c0104822>] sysenter_past_esp+0x5f/0x85
 =======================

This is with 2.6.25-rc6 (SMP) and has been present, as far as I can
remember, since the beginning of the 2.6.25-rc series. It is not
always reproducible, but the trace is always the same.

My filesystem is stored on a ext3 (rw,noatime) dm_crypt'd partition
leaving in a LVM volume.

% lsmod | grep dm | grep -v ' 0 *$'
dm_crypt               14340  1 
crypto_blkcipher       18308  6 ecb,cbc,dm_crypt
dm_mod                 53008  26 dm_crypt,dm_mirror,dm_snapshot

Here is the code I have in dm-table.o:

00001042 <dm_table_unplug_all>:
    1042:       56                      push   %esi
    1043:       53                      push   %ebx
    1044:       8b 98 a0 00 00 00       mov    0xa0(%eax),%ebx
    104a:       8d b0 a0 00 00 00       lea    0xa0(%eax),%esi
    1050:       eb 10                   jmp    1062 <dm_table_unplug_all+0x20>
    1052:       8b 43 10                mov    0x10(%ebx),%eax
    1055:       8b 40 5c                mov    0x5c(%eax),%eax
    1058:       8b 40 34                mov    0x34(%eax),%eax
    105b:       e8 fc ff ff ff          call   105c <dm_table_unplug_all+0x1a>
    1060:       8b 1b                   mov    (%ebx),%ebx
    1062:       8b 03                   mov    (%ebx),%eax
    1064:       0f 1f 40 00             nopl   0x0(%eax)
    1068:       39 f3                   cmp    %esi,%ebx
    106a:       75 e6                   jne    1052 <dm_table_unplug_all+0x10>
    106c:       5b                      pop    %ebx
    106d:       5e                      pop    %esi
    106e:       c3                      ret    

The symbol in 105b call is, after relocation, blk_unplug.

It there anything else I can do to help debugging this?

 Sam
-- 
Samuel Tardieu -- sam@rfc1149.net -- http://www.rfc1149.net/