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[Sergio Callegari <sergio.callegari@xxxxxxxxx>]

Please disregard my previous message.

The bug is definitely there.

In some cases it does not manifest immediately. Conversely, it is quite
frequent to see the IOWAIT close to zero at system startup. Then after a
while the system is up, the IOWAIT jumps for no reason at about 50% and
stays there.

When this happens, nothing is initially reported in dmesg/syslog.
However the system starts showing some issues.

1) Trying to mount the zip drive, namely

sudo mount /dev/sda /mnt/tmp

hangs forever. The process cannot be interrupted. Interestingly, this
happens even if there is no disk in the drive, a situation that the
kernel should see immediately, even before trying the mount action.
When the hang occurs, the kernel starts complaining in dmesg about a
hung process:

[11877.606063] INFO: task mount:14652 blocked for more than 120 seconds.
[11877.606077]       Tainted: P         C OE  3.19.0-18-generic #18-Ubuntu
[11877.606082] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[11877.606088] mount           D ffff88006ad038f8     0 14652  14651 0x00000000
[11877.606099]  ffff88006ad038f8 ffff880062ecebf0 0000000000014200 ffff88006ad03fd8
[11877.606108]  0000000000014200 ffff88011a818000 ffff880062ecebf0 ffff88011fcd4200
[11877.606115]  ffff88006ad03a50 7fffffffffffffff ffff88006ad03a48 ffff880062ecebf0
[11877.606121] Call Trace:
[11877.606139]  [<ffffffff817c4f99>] schedule+0x29/0x70
[11877.606149]  [<ffffffff817c857c>] schedule_timeout+0x20c/0x280
[11877.606161]  [<ffffffff8109ed1d>] ? ttwu_do_activate.constprop.94+0x5d/0x70
[11877.606169]  [<ffffffff810a1c19>] ? try_to_wake_up+0x1e9/0x340
[11877.606178]  [<ffffffff817c6954>] wait_for_completion+0xa4/0x170
[11877.606183]  [<ffffffff810a1de0>] ? wake_up_state+0x20/0x20
[11877.606191]  [<ffffffff8108ef1a>] flush_work+0xea/0x1c0
[11877.606200]  [<ffffffff8108bb10>] ? destroy_worker+0xa0/0xa0
[11877.606206]  [<ffffffff8108f0f8>] __cancel_work_timer+0x98/0x1b0
[11877.606214]  [<ffffffff813949f1>] ? exact_lock+0x11/0x20
[11877.606223]  [<ffffffff81509d72>] ? kobj_lookup+0x112/0x170
[11877.606230]  [<ffffffff813939f0>] ? disk_map_sector_rcu+0x80/0x80
[11877.606237]  [<ffffffff8108f243>] cancel_delayed_work_sync+0x13/0x20
[11877.606243]  [<ffffffff81395991>] disk_block_events+0x81/0x90
[11877.606252]  [<ffffffff8122d64b>] __blkdev_get+0x5b/0x490
[11877.606259]  [<ffffffff8122dac1>] blkdev_get+0x41/0x390
[11877.606266]  [<ffffffff8122de70>] ? blkdev_get_by_dev+0x60/0x60
[11877.606273]  [<ffffffff8122decf>] blkdev_open+0x5f/0x90
[11877.606281]  [<ffffffff811f0d82>] do_dentry_open+0x1d2/0x330
[11877.606288]  [<ffffffff811f1049>] vfs_open+0x49/0x50
[11877.606296]  [<ffffffff81201b47>] do_last+0x227/0x12c0
[11877.606305]  [<ffffffff812041e8>] path_openat+0x88/0x610
[11877.606313]  [<ffffffff8120598a>] do_filp_open+0x3a/0xb0
[11877.606320]  [<ffffffff81212777>] ? __alloc_fd+0xa7/0x130
[11877.606328]  [<ffffffff811f299a>] do_sys_open+0x12a/0x280
[11877.606334]  [<ffffffff810963ef>] ? __put_cred+0x3f/0x60
[11877.606341]  [<ffffffff811f1e70>] ? SyS_access+0x1c0/0x210
[11877.606348]  [<ffffffff811f2b0e>] SyS_open+0x1e/0x20
[11877.606356]  [<ffffffff817c990d>] system_call_fastpath+0x16/0x1b

2) It is impossible to cleanly shutdown the machine.  The shutdown
operation hungs and the machine needs to be reset or switched off

3) It is impossible to install a kernel, since something hangs in the
process at the update-initramfs stage.

Point 3) makes it nasty to test new kernels for the issue.

-- 
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Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1451277

Title:
  Extremely high IOWait and processes hungs after utopic->vivid upgrade

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  On Kubuntu, 64 bit AMD Phenom2 machine with 4 cores, and old (Geoforge 7025) Nvidia graphics.
  Using LVM. Machine also has a 2 disk software raid (mirroring).

  The machine was working fine before the upgrade, now it is almost
  impossible to use it... I see Wait in Top always above 60%; in dmesg
  after a few minutes that the machine is up even if the machine does
  nothing. I see hung processes (typically vgs, but occasionally also
  others).  LVM related commands (e.g. lvdisplay) almost always hung at
  the terminal. I also see in ps some kernel workers almost constantly
  stuck in D state. Also, the machine takes ages to shutdown.

  Issue remains there also if I disable X (switch off the X login
  manager, sddm) and check at the console.

  Sorry I cannot provide details with apport, but the machine has been
  switched off and I will not be able to take it up again before a few
  days from now.

  The symptom I am observing may also be a sign of failing hardware, so
  please leave the bug as unconfirmed until I make some more tests or
  someone provide details on similar issues. In the meantime I would
  like to see if others are experiencing a similar serious issue. Is
  there anything specific that has changed between utopic and vivid, I
  should look into?

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