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While running an Ubuntu kernel (not a mainline or third-party kernel)
please enter the following command in a terminal window:

apport-collect 1732238

and then change the status of the bug to 'Confirmed'.

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This change has been made by an automated script, maintained by the
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** Changed in: linux (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1732238

Title:
  arm64: Unfair rwlock can stall the system

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  [Impact]
  There is a long-standing upstream bug with the ARM64 specific implementation 
of RW locks. The implementation can starve writers under lock contention 
leading to RCU stalls and general system instability.

  [Test Case]
  $ stress-ng --kill 0 -t 300 -v

  You'll see the console fill with messages like:

  [ 2534.423119] INFO: rcu_sched detected stalls on CPUs/tasks:
  [ 2534.428606]        192-...: (1 ticks this GP) idle=b6e/140000000000000/0 
softirq=578/578 fqs=6770 
  [ 2534.437029]        (detected by 0, t=15005 jiffies, g=1479, c=1478, q=473)
  [ 2714.623691] INFO: rcu_sched detected stalls on CPUs/tasks:
  [ 2714.629181]        192-...: (1 ticks this GP) idle=b6e/140000000000000/0 
softirq=578/578 fqs=12819 
  [ 2714.637692]        (detected by 116, t=60058 jiffies, g=1479, c=1478, 
q=1736)
  [ 2747.216955] watchdog: BUG: soft lockup - CPU#0 stuck for 22s! 
[kworker/0:5:1464]
  [ 2775.399061] watchdog: BUG: soft lockup - CPU#13 stuck for 123s! 
[systemd-network:2936]

  [Regression Risk]
  TBD

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