Just saw
commit c7f26ccfb2c31eb1bf810ba13d044fcf583232db
Author: Steven J. Hill <steven.hill@xxxxxxxxxx>
Date: Wed Mar 28 16:01:09 2018 -0700
mm/vmstat.c: fix vmstat_update() preemption BUG
Attempting to hotplug CPUs with CONFIG_VM_EVENT_COUNTERS enabled can
cause vmstat_update() to report a BUG due to preemption not being
disabled around smp_processor_id().
The fix is wrong.
vmstat_update cannot be moved to a differentprocessor and thus
preemption should be off.
vmstat_update repeatedly accesses per cpu information.
vmstat_update first checks if there are counter to be updated on the
current cpu and then updates the counters. This cannot happen if the
process can be moved to a different cpu.
The patch "switches off" preemption after the check if there are changes
to the local per cpu counter.
Lets find out what changed in the callers of vmstat_update() that caused
the BUG to be triggered.
