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, 6 insertions, 4 deletions

diff --git a/sys/kern/kern_jail.c b/sys/kern/kern_jail.c
index e4342ad..b87de0b 100644
--- a/sys/kern/kern_jail.c
+++ b/sys/kern/kern_jail.c
@@ -1529,8 +1529,9 @@ sysctl_jail_list(SYSCTL_HANDLER_ARGS)
 	return (error);
 }
 
-SYSCTL_OID(_security_jail, OID_AUTO, list, CTLTYPE_STRUCT | CTLFLAG_RD,
-    NULL, 0, sysctl_jail_list, "S", "List of active jails");
+SYSCTL_OID(_security_jail, OID_AUTO, list,
+    CTLTYPE_STRUCT | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
+    sysctl_jail_list, "S", "List of active jails");
 
 static int
 sysctl_jail_jailed(SYSCTL_HANDLER_ARGS)
@@ -1542,8 +1543,9 @@ sysctl_jail_jailed(SYSCTL_HANDLER_ARGS)
 
 	return (error);
 }
-SYSCTL_PROC(_security_jail, OID_AUTO, jailed, CTLTYPE_INT | CTLFLAG_RD,
-    NULL, 0, sysctl_jail_jailed, "I", "Process in jail?");
+SYSCTL_PROC(_security_jail, OID_AUTO, jailed,
+    CTLTYPE_INT | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
+    sysctl_jail_jailed, "I", "Process in jail?");
 
 #ifdef DDB
 DB_SHOW_COMMAND(jails, db_show_jails)