Updated 7.4 kernel?

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R37ribution
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Joined: 2018/05/11 14:28:11

Updated 7.4 kernel?

Post by R37ribution » 2018/05/11 14:59:42

I was hoping someone could tell me where (assuming I'm missing it) or if an updated kernel for 7.4 would be released beyond kernel-3.10.0-693.21.1.el7.x86_64.rpm which seems to be the latest in this repo - http://mirror.centos.org/centos/7.4.170 ... /Packages/

The reason I ask is because there is a critical bug related to memory cgroups that was addressed in RH kernel release 3.10.0-693.25.2.el7 (actual update came in as 3.10.0-693.23.1.el7) - from the release notes on RedHat's site:
- [mm] memcg, slab: do not destroy children caches if parent has aliases (Aristeu Rozanski) [1546734 1502818]
- [mm] memcg, slab: fix races in per-memcg cache creation/destruction (Aristeu Rozanski) [1546734 1502818]
- [mm] memcg, slab: clean up memcg cache initialization/destruction (Aristeu Rozanski) [1546734 1502818]
- [mm] memcg, slab: kmem_cache_create_memcg(): fix memleak on fail path (Aristeu Rozanski) [1546734 1502818]

The conditions required to trigger this bug are:
-A service should be associated with a cgroup.
-During start/restart/stop operation it should load or unload any kernel module.

One of the impacts to us is that any time iptables is stopped, we get slab/slub errors that last between 5 and 20 minutes. We basically cannot shutdown the host without this problem. We've successfully worked around this bug by disabling memory cgroups via a kernel paramter "cgroup_disable=memory" but then we cannot run containers which is the purpose of these hosts. There is another service that when stopped causes problems - systemd-readahead-rep.service. If we stop both of these services prior to shutting down the host, the slab/slub errors will occur at service stop and then a shutdown/reboot will happen cleanly.

I realize that the latest 7.5 kernel contains the bugfix, but we're not ready to update to 7.5 just yet as this would require much more testing than a simple kernel update. I'm not sure if it matters, but the 7.5 and 7.4 kernels came out very close to each other. The release 3.10.0-693.25.2.el7 came out around 4/17. I see one more update for 7.4 has come out since then - 3.10.0-693.25.4.el7.

Here are the Bugzilla IDs regarding the memory cgroups issues:
Bug 1502818 - crash within slab/slub when releasing bio slab reference on system where mem cgroups are in use
Bug 1546734 - crash within slab/slub when releasing bio slab reference on system where mem cgroups are in use [rhel-7.4.z]
Bug 1546733 - crash within slab/slub when releasing bio slab reference on system where mem cgroups are in use [rhel-7.3.z]

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avij
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Re: Updated 7.4 kernel?

Post by avij » 2018/05/11 15:13:37

There won't be any new kernels beyond 3.10.0-693.21.1 in CentOS 7.4 (or any other packages for that matter).

Red Hat offers support contracts where you can stay on a specific point releases (z stream), but those updated kernels are not available to the public and thus they are not available in CentOS either.

Yes, you would need to upgrade to 7.5 to get a newer CentOS kernel.

R37ribution
Posts: 4
Joined: 2018/05/11 14:28:11

Re: Updated 7.4 kernel?

Post by R37ribution » 2018/05/18 14:03:25

Thank you for the quick reply!

We're negotiating a support contract with RedHat but, due to our current budget constraints, its a hard sell due to cost per socket pair even at the volume we have. I've worked with them before and their support is nothing short of fantastic. In one instance, the case engineer authored his own code as a suggested resolution to the developer in the bugzilla he created on our behalf. I guess you get what you pay for. I've done my best to justify the RedHat expense.

I thought that perhaps with the severity of the cgroups bug that there would be an update to the CentOS kernel, but if RedHat doesn't make the source code available for 7.4 beyond 693.21.1, there's nothing to build off of.

Again, thanks for your time.
avij wrote:There won't be any new kernels beyond 3.10.0-693.21.1 in CentOS 7.4 (or any other packages for that matter).

Red Hat offers support contracts where you can stay on a specific point releases (z stream), but those updated kernels are not available to the public and thus they are not available in CentOS either.

Yes, you would need to upgrade to 7.5 to get a newer CentOS kernel.

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