kernel: use gettime(9)/getuptime(9) in lieu of time_second(9)/time_uptime(9)

time_second(9) and time_uptime(9) are widely used in the kernel to
quickly get the system UTC or system uptime as a time_t.  However,
time_t is 64-bit everywhere, so it is not generally safe to use them
on 32-bit platforms: you have a split-read problem if your hardware
cannot perform atomic 64-bit reads.

This patch replaces time_second(9) with gettime(9), a safer successor
interface, throughout the kernel.  Similarly, time_uptime(9) is replaced
with getuptime(9).

There is a performance cost on 32-bit platforms in exchange for
eliminating the split-read problem: instead of two register reads you
now have a lockless read loop to pull the values from the timehands.
This is really not *too* bad in the grand scheme of things, but
compared to what we were doing before it is several times slower.

There is no performance cost on 64-bit (__LP64__) platforms.

With input from visa@, dlg@, and tedu@.

Several bugs squashed by visa@.

ok kettenis@

1 files changed, 5 insertions, 5 deletions

diff --git a/sys/kern/sysv_msg.c b/sys/kern/sysv_msg.c
index d518837a6aa..d09e3b32e61 100644
--- a/sys/kern/sysv_msg.c
+++ b/sys/kern/sysv_msg.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sysv_msg.c,v 1.36 2019/12/30 15:48:12 mpi Exp $	*/
+/*	$OpenBSD: sysv_msg.c,v 1.37 2020/06/24 22:03:42 cheloha Exp $	*/
 /*	$NetBSD: sysv_msg.c,v 1.19 1996/02/09 19:00:18 christos Exp $	*/
 /*
  * Copyright (c) 2009 Bret S. Lambert <blambert@openbsd.org>
@@ -168,7 +168,7 @@ msgctl1(struct proc *p, int msqid, int cmd, caddr_t buf,
 		    (que->msqid_ds.msg_perm.mode & ~0777) |
 		    (tmp.msg_perm.mode & 0777);
 		que->msqid_ds.msg_qbytes = tmp.msg_qbytes;
-		que->msqid_ds.msg_ctime = time_second;
+		que->msqid_ds.msg_ctime = gettime();
 		break;
 
 	case IPC_STAT:
@@ -414,7 +414,7 @@ que_create(key_t key, struct ucred *cred, int mode)
 	que->msqid_ds.msg_perm.mode = mode & 0777;
 	que->msqid_ds.msg_perm.seq = ++sequence & 0x7fff;
 	que->msqid_ds.msg_qbytes = msginfo.msgmnb;
-	que->msqid_ds.msg_ctime = time_second;
+	que->msqid_ds.msg_ctime = gettime();
 
 	TAILQ_INIT(&que->que_msgs);
 
@@ -549,7 +549,7 @@ msg_enqueue(struct que *que, struct msg *msg, struct proc *p)
 	que->msqid_ds.msg_cbytes += msg->msg_len;
 	que->msqid_ds.msg_qnum++;
 	que->msqid_ds.msg_lspid = p->p_p->ps_pid;
-	que->msqid_ds.msg_stime = time_second;
+	que->msqid_ds.msg_stime = gettime();
 
 	TAILQ_INSERT_TAIL(&que->que_msgs, msg, msg_next);
 }
@@ -560,7 +560,7 @@ msg_dequeue(struct que *que, struct msg *msg, struct proc *p)
 	que->msqid_ds.msg_cbytes -= msg->msg_len;
 	que->msqid_ds.msg_qnum--;
 	que->msqid_ds.msg_lrpid = p->p_p->ps_pid;
-	que->msqid_ds.msg_rtime = time_second;
+	que->msqid_ds.msg_rtime = gettime();
 
 	TAILQ_REMOVE(&que->que_msgs, msg, msg_next);
 }