[regression, 3.1, rcu] rcu_sched_state detected stall on CPU 8 (t=15000 jiffies)

[Dave Chinner <david@fromorbit.com>]

Hi Paul,

I've had this hang a couple of times now, so I figured it isn't an
isolated event. I am getting kernels occassionally hanging with the
following output occurring:

[   62.812011] INFO: rcu_sched_state detected stall on CPU 8 (t=15000 jiffies)
[  242.936009] INFO: rcu_sched_state detected stall on CPU 8 (t=60031 jiffies)

And that just goes on until I reboot the machine. e.g. from a test
run on a 2p VM that I didn't check on over the weekend:

[220167.108005] INFO: rcu_sched_state detected stall on CPU 0 (t=54681420 jiffies)
[220347.228004] INFO: rcu_sched_state detected stall on CPU 0 (t=54726450 jiffies)
[220527.348003] INFO: rcu_sched_state detected stall on CPU 0 (t=54771480 jiffies)
[220707.468006] INFO: rcu_sched_state detected stall on CPU 0 (t=54816510 jiffies)
[220887.588003] INFO: rcu_sched_state detected stall on CPU 0 (t=54861540 jiffies)
[221067.708003] INFO: rcu_sched_state detected stall on CPU 0 (t=54906570 jiffies)
[221247.828004] INFO: rcu_sched_state detected stall on CPU 0 (t=54951600 jiffies)
[221427.948003] INFO: rcu_sched_state detected stall on CPU 0 (t=54996630 jiffies)
[221608.068003] INFO: rcu_sched_state detected stall on CPU 0 (t=55041660 jiffies)
[221788.188019] INFO: rcu_sched_state detected stall on CPU 0 (t=55086690 jiffies)
[221968.308014] INFO: rcu_sched_state detected stall on CPU 0 (t=55131720 jiffies)
[222148.428010] INFO: rcu_sched_state detected stall on CPU 0 (t=55176750 jiffies)

I've seen it on 2p and now a 16p test VM. This one occurred
during boot of the 16p VM:

[    2.600499] kjournald starting.  Commit interval 5 seconds
[    2.600878] EXT3-fs (sda1): mounted filesystem with ordered data mode
[    2.600995] VFS: Mounted root (ext3 filesystem) readonly on device 8:1.
[    2.612351] Freeing unused kernel memory: 2824k freed
INIT: version 2.88 booting
Using makefile-style concurrent boot in runlevel S.
[   62.812011] INFO: rcu_sched_state detected stall on CPU 8 (t=15000 jiffies)
[  242.936009] INFO: rcu_sched_state detected stall on CPU 8 (t=60031 jiffies)

While the console still echos characters, the boot process is
not making progress.

I've had this happen under heavy CPU and IO load, sometimes hours
after boot e.g. one was mid-way through a 4th run of xfstests which
takes about 80mins to do a complete run. There doesn't appear to be
any pattern to when it occurs and I cannot reproduce it on command,
so tracking it down might be difficult.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com