Userspace starving kernel threads for CPU cycle.

[valdis.kletnieks at vt.edu]

On Fri, 08 Jun 2018 23:05:33 -0500, Àbéjídé Àyodélé said:

> rcu_sched detected stalls on CPUs
> Sending NMI from CPU 43 to CPUs 14
> watchdog: BUG: soft lockup - CPU#26 stuck for 22s [migration/54:335]
> ixgbe 0000:19:00.1 eno2: initiating reset due to tx timeout

The BUG should have caused a stack traceback which would have told us
where the CPU was stuck for 22 seconds.  That's usually not a starvation issue,
it's more often a deadlock (or livelock) condition where the thread on CPU#26 was
waiting for something to happen, and it never happened.
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