PROBLEM: INFO: task apache2:8693 blocked for more than 120 secondswith kernel 3.8.8

[Lilian - Devclic]

Hello,

We upgraded kernel on all system of a cluster and have some troubles 
with Apache 2. The architecture is composed by 4 NFS clients and 1 NFS 
Server, all based on 3.8.8 kernel version ( before, it was 2.6.32 on all 
systems and was running with no problem )

Sometimes and after having reboot on kernel 3.8.8, NFS Clients display 
this trace in the dmesg :

[12100.793549] INFO: task apache2:8695 blocked for more than 120 seconds.
[12100.793577] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" 
disables this message.
[12100.793621] apache2         D 0000000000000002     0  8695   7799 
0x00000000
[12100.793623]  ffff880215309d98 0000000000000086 ffff880215308010 
0000000000013940
[12100.793627]  ffff880215086300 0000000000013940 ffff880215309fd8 
0000000000013940
[12100.793630]  ffff880215309fd8 0000000000013940 ffff8802365418c0 
ffff880215086300
[12100.793633] Call Trace:
[12100.793636]  [<ffffffff815681f6>] schedule+0x64/0x66
[12100.793640]  [<ffffffff8156843e>] schedule_preempt_disabled+0xe/0x10
[12100.793643]  [<ffffffff81567190>] __mutex_lock_common+0x11d/0x18b
[12100.793646]  [<ffffffff8113dc27>] ? filename_lookup+0x74/0x84
[12100.793649]  [<ffffffff81567219>] __mutex_lock_slowpath+0x1b/0x1d
[12100.793652]  [<ffffffff81566fd5>] mutex_lock+0x1b/0x2c
[12100.793655]  [<ffffffff8113e76d>] do_unlinkat+0x92/0x231
[12100.793659]  [<ffffffff81131d7e>] ? fsnotify_access+0x5d/0x65
[12100.793662]  [<ffffffff81132f23>] ? sys_read+0x81/0x8e
[12100.793665]  [<ffffffff8113e922>] sys_unlink+0x16/0x18
[12100.793668]  [<ffffffff81570259>] system_call_fastpath+0x16/0x1b

The NFS Server exports a filesystem formatted in ReiserFS ( we mean it 
was the problem ) and we migrate to ext4, the problem is always present. 
I have one other architecture with a NFS Server based on a 2.6.24 Kernel 
and some clients with a 3.8.8 Kernel, the problem doesn't appear.

We made some tests with a 3.2 kernel and it was the same problem.

Can you give me some help ?

Thanks a lot.
Best Regards.
--
Lilian RIGARD - Devclic
Gérant - CEO & CTO
E-mail : lilian@xxxxxxxxxx <mailto:lilian@xxxxxxxxxx>
Web : http://www.devclic.fr
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