[Bug 606324] [NEW] System freeze with "Clocksource tsc unstable" reported *after* freeze

Ian Macintosh 606324 at bugs.launchpad.net
Fri Jul 16 15:08:11 UTC 2010

Public bug reported:

Jul 16 09:36:23 pvmh01 kernel: [1266749.547022] Clocksource tsc unstable
(delta = 515402906059 ns)

The system froze up for the indicated 8.59 minutes as accurately as I
can tell.

I've done some research on this through other bug reports but find a
seemingly opposite issue to those with 'tsc unstable' who report that
the message occurs before the system freezes up.  But that might be an
incorrect observation on their part?

A more completely relevant /var/log/messages extract:

Jul 16 08:55:56 pvmh01 -- MARK --
Jul 16 09:15:56 pvmh01 -- MARK --
Jul 16 09:35:56 pvmh01 -- MARK --
Jul 16 09:36:23 pvmh01 kernel: [1266749.547022] Clocksource tsc unstable (delta = 515402906059 ns)
Jul 16 09:55:56 pvmh01 -- MARK --
Jul 16 10:15:56 pvmh01 -- MARK --
Jul 16 10:35:56 pvmh01 -- MARK --

I need to elaborate on the freeze as it wasn't a complete freeze.  I
logged in via SSH on a session about 6 minutes into the freeze, but
couldn't open a second session.  The second and subsequent SSH
connection attempts hung for another 2 1/2 minutes when suddenly
everything unfroze and the other 5 sessions I was trying to establish

In previous instances where this and other servers had frozen (all
running Ubuntu 8.04.4) I had often succeeded in logging on once, but it
seemed that any attempt to execute a command that resulted in disk
access would freeze and leave the SSH session locked and unusable, not
even able to background the stalled task.  Where I had been fortunate
enough to get more than one SSH session logged in, even killing the PID
with -TERM wouldn't unfreeze the other terminal.

This is however the first time I have suddenly had the server unfreeze
on me and everything returned to normal with the only blip on the radar
being the 'tsc unstable' report.

This is not caused by dirty_background_ratio hitting ceiling and
freezing the system while it writes hundreds of thousands of blocks to
the disk.  /proc/vmstat nr_dirty and nr_writeback were normal.  I've
double-crossed that bridge before.

I'm very suspicious that it has _something_ to do with the software disk
subsystem, but I could be cherry picking because I don't trust the new
'improved' cache system that replaced the simple old Linus elevator.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

System freeze with "Clocksource tsc unstable" reported *after* freeze
You received this bug notification because you are a member of Kernel
Bugs, which is subscribed to linux in ubuntu.

More information about the kernel-bugs mailing list