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Bug 145976

Summary: Sub-second mtime changes without modifying file
Product: Red Hat Enterprise Linux 4 Reporter: Stephen Tweedie <sct>
Component: kernelAssignee: Stephen Tweedie <sct>
Status: CLOSED ERRATA QA Contact: Brian Brock <bbrock>
Severity: medium Docs Contact:
Priority: medium    
Version: 4.0CC: ajschult784, davej, jbaron, riel, tburke
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: RHSA-2005-514 Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2005-10-05 12:42:29 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:
Bug Depends On:    
Bug Blocks: 139847, 154907, 156322    
Attachments:
Description Flags
Upstream 2.6 patch to implement fs-specific timestamp granularities none

Description Stephen Tweedie 2005-01-24 14:17:52 UTC 
*** This bug has been split off bug 139884 ***

------- Original comment by Patrick J. LoPresti on 2004.11.18 12:05 -------

From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.5)
Gecko/20041111 Firefox/1.0

Description of problem:
The 2.6 kernel's buffer cache has sub-second resolution for file
times.  The ext3 file system does not.  Consequently, the observable
mtime for a file changes unpredictably.

This is causing problems for us while compiling our product, because
"make" relies on file modification times to determine what to compile.
 But the bug is easily observed without running make; see the steps below.


Version-Release number of selected component (if applicable):
kernel-2.6.9-1.678_FC3

How reproducible:
Always

Steps to Reproduce:
1. touch /tmp/foo

2. ls -l --full-time /tmp/foo

3. (reboot system)

4. ls -l --full-time /tmp/foo

    

Actual Results:  The visible file modification time changes (gets
rounded down) as a result of the reboot.  The rounding down happens
whenever the kernel's buffer cache for the file gets flushed, which on
an active system is essentially random.


Expected Results:  The file modification time should not change for a
file which is not modified.


Additional info:

This was discussed on the linux-kernel mailing list back in April, but
as far as I can tell it was never resolved:

  http://www.ussg.iu.edu/hypermail/linux/kernel/0404.0/0193.html

And now it is causing a real problem for us.  This is clearly a kernel
bug; a file's modification time should not change unless the file is
modified.
Comment 2 Stephen Tweedie 2005-01-24 14:23:21 UTC 
Created attachment 110123 [details]
Upstream 2.6 patch to implement fs-specific timestamp granularities
Comment 13 Stephen Tweedie 2005-09-30 15:38:26 UTC 
*** Bug 155406 has been marked as a duplicate of this bug. ***
Comment 15 Red Hat Bugzilla 2005-10-05 12:42:29 UTC 
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2005-514.html