[CentOS] maintaining patches across releases

[Keith Keller]

Hi all,

I have what might be a foolish question about patching packages.  I am
not sure exactly how to phrase the question, so please follow up if it
seems as though I'm not being clear.

I was looking at this bug which my machines are currently experiencing:

https://bugzilla.redhat.com/show_bug.cgi?id=883905

The proposed patch is literally one new line in the XFS codebase.  So
since the patch is so straightforward, I had a crazy idea that I would
build my own kernel with this patch, and test it out to see if it
worked.  (It's been many years since I built my own kernel, so that
would be an adventure in and of itself.)

My worry would be, I would want to make sure that I propagated this
patch every time I updated the kernel package.  Is this something
others do regularly?  If so, is there a standard way of managing
the process of applying one's own patches to a series of source
packages, and being able to re-patch and rebuild updated packages?

I'm guessing that I just need to build xfs.ko.  Are there any gotchas
beyond the wiki entry on building your own kernel modules?  That page
seems to target CentOS 5, not 6, but I imagine the process is quite
similar.

--keith

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Re: [CentOS] maintaining patches across releases

[Akemi Yagi]

On Wed, Mar 6, 2013 at 3:22 PM, Keith Keller
 wrote:
> Hi all,
>
> I have what might be a foolish question about patching packages.  I am
> not sure exactly how to phrase the question, so please follow up if it
> seems as though I'm not being clear.
>
> I was looking at this bug which my machines are currently experiencing:
>
> https://bugzilla.redhat.com/show_bug.cgi?id=883905
>
> The proposed patch is literally one new line in the XFS codebase.  So
> since the patch is so straightforward, I had a crazy idea that I would
> build my own kernel with this patch, and test it out to see if it
> worked.  (It's been many years since I built my own kernel, so that
> would be an adventure in and of itself.)

You may want to check this out:

http://bugs.centos.org/view.php?id=6087

My understanding is that "There is no side effect other than the load.
There are not performance issues with the ailds behaving like this."
Is this not the case ?

> My worry would be, I would want to make sure that I propagated this
> patch every time I updated the kernel package.  Is this something
> others do regularly?  If so, is there a standard way of managing
> the process of applying one's own patches to a series of source
> packages, and being able to re-patch and rebuild updated packages?
>
> I'm guessing that I just need to build xfs.ko.  Are there any gotchas
> beyond the wiki entry on building your own kernel modules?  That page
> seems to target CentOS 5, not 6, but I imagine the process is quite
> similar.
>
> --keith

The wiki article:

http://wiki.centos.org/HowTos/BuildingKernelModules

may not be quite up-to-date in that it does not reflect the kernel
version for CentOS 6 (2.6.32). But the principle is there. For
building your own modules, you can also download one of the kmod
packages from ELRepo and study how it's done.

Akemi
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Re: [CentOS] maintaining patches across releases

[Keith Keller]

On 2013-03-07, Akemi Yagi  wrote:
>
> You may want to check this out:
>
> http://bugs.centos.org/view.php?id=6087
>
> My understanding is that "There is no side effect other than the load.
> There are not performance issues with the ailds behaving like this."
> Is this not the case ?

As far as I can tell, it is.  I actually prompted Dave's quoted comment
on the XFS list:

http://oss.sgi.com/archives/xfs/2012-11/msg00594.html

So this would be a low priority task for me (as well as a learning
exercise).  If the patch were two lines I probably wouldn't bother.  ;-)
It is 99.5% cosmetic, but I have noticed that the ''baseline'' load,
when there is no I/O, varies between 3 and 4, which makes it very
slightly more difficult to interpret the load.  That is my main
motivation for bothering--if the baseline were more stable I probably
wouldn't bother.  (With fewer XFS filesystems mounted the issue is
even less obvious.)

> The wiki article:
>
> http://wiki.centos.org/HowTos/BuildingKernelModules
>
> may not be quite up-to-date in that it does not reflect the kernel
> version for CentOS 6 (2.6.32). But the principle is there. For
> building your own modules, you can also download one of the kmod
> packages from ELRepo and study how it's done.

Perfect, thank you!  If people are interested, and I do make the
attempt, I will post my results.

--keith

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Re: [CentOS] maintaining patches across releases

[Akemi Yagi]

On Wed, Mar 6, 2013 at 4:25 PM, Keith Keller
 wrote:
> On 2013-03-07, Akemi Yagi  wrote:
>>
>> You may want to check this out:
>>
>> http://bugs.centos.org/view.php?id=6087
>>
>> My understanding is that "There is no side effect other than the load.
>> There are not performance issues with the ailds behaving like this."
>> Is this not the case ?
>
> As far as I can tell, it is.  I actually prompted Dave's quoted comment
> on the XFS list:
>
> http://oss.sgi.com/archives/xfs/2012-11/msg00594.html
>
> So this would be a low priority task for me (as well as a learning
> exercise).  If the patch were two lines I probably wouldn't bother.  ;-)
> It is 99.5% cosmetic, but I have noticed that the ''baseline'' load,
> when there is no I/O, varies between 3 and 4, which makes it very
> slightly more difficult to interpret the load.  That is my main
> motivation for bothering--if the baseline were more stable I probably
> wouldn't bother.  (With fewer XFS filesystems mounted the issue is
> even less obvious.)

I thought about applying the patch to the centosplus kernel but
decided not to bother because it looked like a "non-issue". But it you
think it's worth the fix, that can be done. It will be even better if
you supply the actual patch for the CentOS kernel.

Akemi
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Re: [CentOS] maintaining patches across releases

[Keith Keller]

On 2013-03-07, Akemi Yagi  wrote:
>
> I thought about applying the patch to the centosplus kernel but
> decided not to bother because it looked like a "non-issue". But it you
> think it's worth the fix, that can be done. It will be even better if
> you supply the actual patch for the CentOS kernel.

Honestly I do not think it's worth the fix for the centosplus kernel.
But perhaps others disagree with me; if so, is the proposed patch by
RedHat usable?

https://bugzilla.redhat.com/attachment.cgi?id=674895

If it's not, let me know, and I will try to generate the correct one.

--keith

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Re: [CentOS] maintaining patches across releases

[Akemi Yagi]

On Wed, Mar 6, 2013 at 8:16 PM, Keith Keller
 wrote:
> On 2013-03-07, Akemi Yagi  wrote:
>>
>> I thought about applying the patch to the centosplus kernel but
>> decided not to bother because it looked like a "non-issue". But it you
>> think it's worth the fix, that can be done. It will be even better if
>> you supply the actual patch for the CentOS kernel.
>
> Honestly I do not think it's worth the fix for the centosplus kernel.
> But perhaps others disagree with me; if so, is the proposed patch by
> RedHat usable?
>
> https://bugzilla.redhat.com/attachment.cgi?id=674895
>
> If it's not, let me know, and I will try to generate the correct one.
>
> --keith

I looked at the patch again -- it was apparently not for the 6.3
kernel and I was not 100% sure about applying it at that time. But now
with the 6.4 kernel, it cleanly applies.

While not serious, some users are finding this bug to be problematic
when monitoring the stats. I will include the fix in the next plus
kernel update.

Akemi
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Re: [CentOS] maintaining patches across releases

[Keith Keller]

On 2013-03-08, Akemi Yagi  wrote:
>
> I looked at the patch again -- it was apparently not for the 6.3
> kernel and I was not 100% sure about applying it at that time. But now
> with the 6.4 kernel, it cleanly applies.
>
> While not serious, some users are finding this bug to be problematic
> when monitoring the stats. I will include the fix in the next plus
> kernel update.

That's great, thanks!  I'll keep my eye on the repo.

In previous versions, the centosplus additions were documented in a readme
file at the top level of the centosplus directory.  Are there similar
docs for CentOS 6?  I checked the wiki and the ftp sites but didn't find
anything yet.

--keith

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Re: [CentOS] maintaining patches across releases

[Akemi Yagi]

On Fri, Mar 8, 2013 at 2:11 PM, Keith Keller
 wrote:
> On 2013-03-08, Akemi Yagi  wrote:
>>
>> I looked at the patch again -- it was apparently not for the 6.3
>> kernel and I was not 100% sure about applying it at that time. But now
>> with the 6.4 kernel, it cleanly applies.
>>
>> While not serious, some users are finding this bug to be problematic
>> when monitoring the stats. I will include the fix in the next plus
>> kernel update.
>
> That's great, thanks!  I'll keep my eye on the repo.
>
> In previous versions, the centosplus additions were documented in a readme
> file at the top level of the centosplus directory.  Are there similar
> docs for CentOS 6?  I checked the wiki and the ftp sites but didn't find
> anything yet.

The only place the plus kernels are "documented" with up-to-date info
is the CentOS bug tracker:

CentOS-6: http://bugs.centos.org/view.php?id=4586
CentOS-5: http://bugs.centos.org/view.php?id=4100

Akemi
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Re: [CentOS] maintaining patches across releases

[Keith Keller]

On 2013-03-08, Akemi Yagi  wrote:
>
> The only place the plus kernels are "documented" with up-to-date info
> is the CentOS bug tracker:
>
> CentOS-6: http://bugs.centos.org/view.php?id=4586
> CentOS-5: http://bugs.centos.org/view.php?id=4100

That's perfect.  It seems completely reasonable to suggest to people who
want to fix this issue to use the centosplus kernel when it comes out
instead; I don't see anything that would block most systems from deploying
it.  Of course I will still try it on a non-critical system first.  :)

--keith


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Re: [CentOS] maintaining patches across releases

[Keith Keller]

On 2013-03-08, Akemi Yagi  wrote:
>
> The only place the plus kernels are "documented" with up-to-date info
> is the CentOS bug tracker:
>
> CentOS-6: http://bugs.centos.org/view.php?id=4586

At least for CentOS 6 it looks like the new centosplus kernel is out.
Thanks Akemi!  I have it running on a test box, and it looks like it
properly addresses the XFS aild issue.  If you want to address this
issue and don't feel like managing dkms, it might be worth your while to
test out the centosplus kernel on your own machines.

--keith

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Re: [CentOS] maintaining patches across releases

[Akemi Yagi]

On Wed, Mar 13, 2013 at 12:24 PM, Keith Keller
 wrote:
> On 2013-03-08, Akemi Yagi  wrote:
>>
>> The only place the plus kernels are "documented" with up-to-date info
>> is the CentOS bug tracker:
>>
>> CentOS-6: http://bugs.centos.org/view.php?id=4586
>
> At least for CentOS 6 it looks like the new centosplus kernel is out.
> Thanks Akemi!  I have it running on a test box, and it looks like it
> properly addresses the XFS aild issue.  If you want to address this
> issue and don't feel like managing dkms, it might be worth your while to
> test out the centosplus kernel on your own machines.
>
> --keith

Thanks for reporting back with the confirmation that the patch fixed the issue.

Akemi
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Re: [CentOS] maintaining patches across releases

[James Pearson]

Keith Keller wrote:
> I was looking at this bug which my machines are currently experiencing:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=883905
> 
> The proposed patch is literally one new line in the XFS codebase.  So
> since the patch is so straightforward, I had a crazy idea that I would
> build my own kernel with this patch, and test it out to see if it
> worked.  (It's been many years since I built my own kernel, so that
> would be an adventure in and of itself.)

Looks like this problem will be fix in kernel-2.6.32-358.5.1.el6 - see 


James Pearson
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