Bug 1293229

Summary: RCU stalls message on realtime kernel
Product: Red Hat Enterprise Linux 7 Reporter: Jan Kurik <jkurik>
Component: kernel-rtAssignee: Luis Claudio R. Goncalves <lgoncalv>
kernel-rt sub component: Process management QA Contact:
Status: CLOSED ERRATA Docs Contact:
Severity: high    
Priority: high CC: bhu, daolivei, jkastner, lgoncalv, williams
Version: 7.3Keywords: ZStream
Target Milestone: rc   
Target Release: ---   
Hardware: x86_64   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
Cause: A possible livelock in the NAPI polling and busy polling routines could lead the system to a livelock on threads running at high, realtime, priorities. Consequence: threads running at priorities lower than the ones of the threads involved in the livelock would be prevented from running on the CPUs affected by the livelock. Among those threads are the rcuc/ threads. Fix: right before (4 jiffies) a RCU stall is detected, the rcuc/ threads on the CPUs facing the livelock have their priorities boosted above the priority of the threads involved in the livelock. Also, the softirqs are now handled in a way closer to the behavior of the upstream kernel. Result: Even under pressure thre rcuc/ threads are able to run, mitigating the RCU stalls.
 Story Points: ---
Clone Of: 1292927
: 1295885 (view as bug list) Environment:
Last Closed: 2016-02-16 10:49:54 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: 1292927    
Bug Blocks: 1295885    
Attachments:
Description Flags
rcu: Boost rcuc if it has 4 jiffies before splatting
none
softirq: Perform softirqs in local_bh_enable() for a limited amount of time none

Description Jan Kurik 2015-12-21 07:06:33 UTC 
This bug has been copied from bug #1292927 and has been proposed
to be backported to 7.2 z-stream (EUS).
Comment 3 Luis Claudio R. Goncalves 2016-01-07 04:01:31 UTC 
Created attachment 1112334 [details]
rcu: Boost rcuc if it has 4 jiffies before splatting
Comment 4 Luis Claudio R. Goncalves 2016-01-07 04:02:18 UTC 
Created attachment 1112335 [details]
softirq: Perform softirqs in local_bh_enable() for a limited amount of time
Comment 9 errata-xmlrpc 2016-02-16 10:49:54 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, 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://rhn.redhat.com/errata/RHSA-2016-0212.html