sysctl lock in RELENG_6

[Eugene Grosbein]

Hi!

I've RELENG_6 system controlling local PBX through RS-232 port, sio(4).
It also runs syslogd, cron, sshd, bsnmpd and sendmail for outgoing reports.

It locks very often: it answers to pings but PBX controlling software stops
responding, local and remote login attempts hang due to 'login' process
stuck in 'sysctl lock' state. Local consoles do switch with 'Alt-Fn'
and DDB works. It shows that sendmail is in 'sysctl lock' state too.

This is NanoBSD installation running from IDE flash, it's swapless
but I think I could manage to obtain crashdump if there is an interest of it.

I've digged commit logs a bit and found this change MFC'd to RELENG_7
but not RELENG_6:

http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/kern/kern_sysctl.c#rev1.177.6.2

It seems RELENG_6 needs this too, doesn't it?
I'm going to merge the change to RELENG_6 and give it a try.

Eugene Grosbein