Mark most often used sysctl's as MPSAFE.

After running a `make buildkernel', I noticed most of the Giant locks in
sysctl are only caused by a very small amount of sysctl's:

- sysctl.name2oid. This one is locked by SYSCTL_LOCK, just like
  sysctl.oidfmt.

- kern.ident, kern.osrelease, kern.version, etc. These are just constant
  strings.

- kern.arandom, used by the stack protector. It is already protected by
  arc4_mtx.

I also saw the following sysctl's show up. Not as often as the ones
above, but still quite often:

- security.jail.jailed. Also mark security.jail.list as MPSAFE. They
  don't need locking or already use allprison_lock.

- kern.devname, used by devname(3), ttyname(3), etc.

This seems to reduce Giant locking inside sysctl by ~75% in my primitive
test setup.

1 files changed, 4 insertions, 3 deletions

diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index ed14760..515204f 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -773,8 +773,8 @@ sysctl_sysctl_name2oid(SYSCTL_HANDLER_ARGS)
 	return (error);
 }
 
-SYSCTL_PROC(_sysctl, 3, name2oid, CTLFLAG_RW|CTLFLAG_ANYBODY, 0, 0, 
-	sysctl_sysctl_name2oid, "I", "");
+SYSCTL_PROC(_sysctl, 3, name2oid, CTLFLAG_RW|CTLFLAG_ANYBODY|CTLFLAG_MPSAFE,
+    0, 0, sysctl_sysctl_name2oid, "I", "");
 
 static int
 sysctl_sysctl_oidfmt(SYSCTL_HANDLER_ARGS)
@@ -796,7 +796,8 @@ sysctl_sysctl_oidfmt(SYSCTL_HANDLER_ARGS)
 }
 
 
-static SYSCTL_NODE(_sysctl, 4, oidfmt, CTLFLAG_RD, sysctl_sysctl_oidfmt, "");
+static SYSCTL_NODE(_sysctl, 4, oidfmt, CTLFLAG_RD|CTLFLAG_MPSAFE,
+    sysctl_sysctl_oidfmt, "");
 
 static int
 sysctl_sysctl_oiddescr(SYSCTL_HANDLER_ARGS)