ext4dist strange timings on ubuntu 16.04

[Colin Ian King]

Reference: https://github.com/iovisor/bcc/issues/790

"The bug is: timekeeping: Avoid taking lock in NMI path with CONFIG_DEBUG_TIMEKEEPING

The fix is: timekeeping: Fix __ktime_get_fast_ns() regression

Looks like that kernel version has the bug but not the fix. http://changelogs.ubuntu.com/changelogs/pool/main/l/linux/linux_4.4.0-45.66/changelog"

Apparently this is fixed by commit:

commit 58bfea9532552d422bde7afa207e1a0f08dffa7d
Author: John Stultz <email address hidden>
Date: Tue Oct 4 19:55:48 2016 -0700
timekeeping: Fix __ktime_get_fast_ns() regression

[Colin Ian King (colin-king)]

OK, looks like this has been picked up in the stable updates process and is committed to Xenial:

https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/xenial/commit/?h=master-next&id=a826ba085c671d880ac2b3971b5090e973761846

[Scott Emmons (lscotte)]

It's been a few weeks - is there any update when this fix will be published? Thanks!

[Colin Ian King (colin-king)]

So the fix apparently landed in Xenial updates under a generic updates bug number:

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1624037

The commit in Xenial is:

commit 8faecee97860f66fdcc67de58803b1fb4e0b0848
Author: John Stultz <email address hidden>
Date: Tue Aug 23 16:08:21 2016 -0700

Hence I'm going to mark this as fix released.

[Scott Emmons (lscotte)]

Awesome, thanks Colin!

[Scott Emmons (lscotte)]

Actually, I believe it has not been released yet. The fix is in the changelog for 4.4.0-48.69, but the latest release of the xenial LTS kernel is 4.4.0-47.68 where the bug can still be reproduced.

Specifically:
  * Xenial update to v4.4.25 stable release (LP: #1634153)
    - timekeeping: Fix __ktime_get_fast_ns() regression

[Scott Emmons (lscotte)]

The fix for this has really been released this time. Confirmed fixed in 4.4.0-51.72.