kern/54978: cpu_need_proftick() can zap l_pflag

[ad%netbsd.org@localhost]

>Number:         54978
>Category:       kern
>Synopsis:       cpu_need_proftick() can zap l_pflag
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Feb 17 22:05:00 +0000 2020
>Originator:     Andrew Doran
>Release:        NetBSD-current
>Organization:
	The NetBSD Project
>Environment:
NetBSD
Architecture: x86_64
Machine: amd64
>Description:
	cpu_need_proftick() looks like it ORs a value into curlwp->l_pflag
	from the context of statclock(), which it's assumed can fire @
	IPL_HIGH.  l_pflag is only for update by the LWP itself or when the
	LWP is known off the CPU.
>How-To-Repeat:
	Code inspection.
>Fix:
	Yes please.