Bug 1894587

Summary: lru-add-drain workqueue on RT is allocated without being used
Product: Red Hat Enterprise Linux 7 Reporter: Juri Lelli <jlelli>
Component: kernel-rtAssignee: Juri Lelli <jlelli>
kernel-rt sub component: Memory Management QA Contact: Mark Simmons <msimmons>
Status: CLOSED ERRATA Docs Contact:
Severity: medium    
Priority: unspecified CC: bhu, crwood, mm-maint, mstowell, rt-maint, rt-qe
Version: 7.9Keywords: Triaged
Target Milestone: rc   
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Hardware: x86_64   
OS: Linux   
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Last Closed: 2021-06-08 22:33:36 UTC Type: Bug
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Description Juri Lelli 2020-11-04 15:00:45 UTC 
Description of problem:
A customer (AltioStar, this is related to bz1886312) asked for clarifications about
lru-add-drain kthread. They were worried that it might cause latency spikes on isolated
cpus, as its affinity cannot be restricted to non-isolated cpus.

Investigation showed that, on RT kernel, this kthread is allocated (by the workqueue
subsystem), but never actually used since RT kernel doesn't use workqueues to perform
remote_lru_add_drain.

Even though there is practically no harm in creating such kthread, it would be good to
remove it as it creates confusion (at least).

Version-Release number of selected component (if applicable):
kernel-rt-3.10.0-1160.7.1.rt56.1140.el7
Comment 2 Juri Lelli 2020-11-04 15:15:26 UTC 
Fix posted

http://post-office.corp.redhat.com/archives/kernel-rt-team/2020-November/msg00005.html
Comment 23 errata-xmlrpc 2021-06-08 22:33:36 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (Important: kernel-rt security and bug fix update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2021:2316