Bug 445713

Summary: tsc going back bug
Product: Red Hat Enterprise Linux 5 Reporter: Alok Kataria <akataria>
Component: kernelAssignee: Red Hat Kernel Manager <kernel-mgr>
Status: CLOSED DUPLICATE QA Contact: Martin Jenner <mjenner>
Severity: low Docs Contact:
Priority: low    
Version: 5.1CC: dhecht, srihan, tglx
Target Milestone: rcKeywords: Reopened
Target Release: ---   
Hardware: i386   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
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Clone Of: Environment:
Last Closed: 2008-05-27 17:55:09 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Attachments:
Description Flags
fix for tsc going back problem. none

Description Alok Kataria 2008-05-08 18:10:57 UTC 
Description of problem:

There were a few recent reports of tsc going back on LKML, as a result of which
there could be cases when time (gettimeofday) jumps in the future.
http://lkml.org/lkml/2007/8/23/96
http://lkml.org/lkml/2008/3/31/23

I did some kernel instrumentation on the recent RHEL5.1 kernel 
2.6.18-53.1.19.el5, and see that read_tsc does jump back once in a while on my
dual core box. As a result the value returned from read_tsc <
clocksource->cycle_last value, which results in large values of offset due to
the unsigned arithmetic involved (have a look at update_wall_time). Eventually
results in some bogus gettimeofday values.

There was a fix for this problem from Thomas Gleixner which was included in the
2.6.26-rc1 tree. 
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=d8bb6f4c1670c8324e4135c61ef07486f7f17379

Attached is a backport of this fix. This is required on all RHEL kernels that
use clocksource. 

Version-Release number of selected component (if applicable):


How reproducible:


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Additional info:
Comment 1 Alok Kataria 2008-05-08 18:10:57 UTC 
Created attachment 304882 [details]
fix for tsc going back problem.
Comment 2 Prarit Bhargava 2008-05-12 12:53:22 UTC 

*** This bug has been marked as a duplicate of 443435 ***
Comment 3 Alok Kataria 2008-05-12 23:21:30 UTC 
(In reply to comment #2)
> 
> *** This bug has been marked as a duplicate of 443435 ***

I am not authorized to access that BUG, 
It says

"You are not authorized to access bug #443435.

Access to some bugs is restricted due to embargoed security issues or respect
for customer and partner information which must remain confidential."

Is there a way that I can look at that BUG ? Maybe you can add me to the CC list
for bug #443435 ?

Thanks,
Alok
Comment 4 Alok Kataria 2008-05-15 01:14:23 UTC 
(In reply to comment #2)
> 
> *** This bug has been marked as a duplicate of 443435 ***

Prarit,

Let me know if there is anyway to access that bug #443435.
Comment 5 Alok Kataria 2008-05-16 00:49:30 UTC 
Still need access to bug #443435
Need to know if you guys already have the fix and if so which kernel release is
going to have that fix.

Thanks,
Alok

(In reply to comment #3)
> (In reply to comment #2)
> > 
> > *** This bug has been marked as a duplicate of 443435 ***
> 
> I am not authorized to access that BUG, 
> It says
> 
> "You are not authorized to access bug #443435.
> 
> Access to some bugs is restricted due to embargoed security issues or respect
> for customer and partner information which must remain confidential."
> 
> Is there a way that I can look at that BUG ? Maybe you can add me to the CC list
> for bug #443435 ?
> 
> Thanks,
> Alok
Comment 6 Prarit Bhargava 2008-05-27 17:55:09 UTC 
Alok, the latest RHEL5 kernel has this patch.

P.

*** This bug has been marked as a duplicate of 443435 ***