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@

5 files changed, 19 insertions, 19 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);
 }
diff --git a/sys/kern/sysv_sem.c b/sys/kern/sysv_sem.c
index b2222ba92ba..f9dc776842b 100644
--- a/sys/kern/sysv_sem.c
+++ b/sys/kern/sysv_sem.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sysv_sem.c,v 1.57 2020/01/08 15:03:10 mpi Exp $	*/
+/*	$OpenBSD: sysv_sem.c,v 1.58 2020/06/24 22:03:42 cheloha Exp $	*/
 /*	$NetBSD: sysv_sem.c,v 1.26 1996/02/09 19:00:25 christos Exp $	*/
 
 /*
@@ -293,7 +293,7 @@ semctl1(struct proc *p, int semid, int semnum, int cmd, union semun *arg,
 		semaptr->sem_perm.gid = sbuf.sem_perm.gid;
 		semaptr->sem_perm.mode = (semaptr->sem_perm.mode & ~0777) |
 		    (sbuf.sem_perm.mode & 0777);
-		semaptr->sem_ctime = time_second;
+		semaptr->sem_ctime = gettime();
 		break;
 
 	case IPC_STAT:
@@ -478,7 +478,7 @@ sys_semget(struct proc *p, void *v, register_t *retval)
 		    (semseqs[semid] + 1) & 0x7fff;
 		semaptr_new->sem_nsems = nsems;
 		semaptr_new->sem_otime = 0;
-		semaptr_new->sem_ctime = time_second;
+		semaptr_new->sem_ctime = gettime();
 		sema[semid] = semaptr_new;
 		semtot += nsems;
 	} else {
@@ -743,7 +743,7 @@ done:
 		semptr->sempid = p->p_p->ps_pid;
 	}
 
-	semaptr->sem_otime = time_second;
+	semaptr->sem_otime = gettime();
 
 	/* Do a wakeup if any semaphore was up'd. */
 	if (do_wakeup) {
diff --git a/sys/kern/sysv_shm.c b/sys/kern/sysv_shm.c
index 96c5abeea75..1fd99f5b95d 100644
--- a/sys/kern/sysv_shm.c
+++ b/sys/kern/sysv_shm.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sysv_shm.c,v 1.76 2020/03/04 08:04:48 anton Exp $	*/
+/*	$OpenBSD: sysv_shm.c,v 1.77 2020/06/24 22:03:42 cheloha Exp $	*/
 /*	$NetBSD: sysv_shm.c,v 1.50 1998/10/21 22:24:29 tron Exp $	*/
 
 /*
@@ -169,7 +169,7 @@ shm_delete_mapping(struct vmspace *vm, struct shmmap_state *shmmap_s)
 	end = round_page(shmmap_s->va+shmseg->shm_segsz);
 	uvm_unmap(&vm->vm_map, trunc_page(shmmap_s->va), end);
 	shmmap_s->shmid = -1;
-	shmseg->shm_dtime = time_second;
+	shmseg->shm_dtime = gettime();
 	if ((--shmseg->shm_nattch <= 0) &&
 	    (shmseg->shm_perm.mode & SHMSEG_REMOVED)) {
 		shm_deallocate_segment(shmseg);
@@ -286,7 +286,7 @@ sys_shmat(struct proc *p, void *v, register_t *retval)
 	shmmap_s->va = attach_va;
 	shmmap_s->shmid = SCARG(uap, shmid);
 	shmseg->shm_lpid = p->p_p->ps_pid;
-	shmseg->shm_atime = time_second;
+	shmseg->shm_atime = gettime();
 	*retval = attach_va;
 	return (0);
 }
@@ -331,7 +331,7 @@ sys_shmctl(struct proc *p, void *v, register_t *retval)
 		shmseg->shm_perm.mode =
 		    (shmseg->shm_perm.mode & ~ACCESSPERMS) |
 		    (inbuf.shm_perm.mode & ACCESSPERMS);
-		shmseg->shm_ctime = time_second;
+		shmseg->shm_ctime = gettime();
 		break;
 	case IPC_RMID:
 		if ((error = ipcperm(cred, &shmseg->shm_perm, IPC_M)) != 0)
@@ -449,7 +449,7 @@ shmget_allocate_segment(struct proc *p,
 	shmseg->shm_cpid = p->p_p->ps_pid;
 	shmseg->shm_lpid = shmseg->shm_nattch = 0;
 	shmseg->shm_atime = shmseg->shm_dtime = 0;
-	shmseg->shm_ctime = time_second;
+	shmseg->shm_ctime = gettime();
 	shmseg->shm_internal = shm_handle;
 
 	*retval = IXSEQ_TO_IPCID(segnum, shmseg->shm_perm);
diff --git a/sys/kern/vfs_sync.c b/sys/kern/vfs_sync.c
index 9a9231a3eee..62693a1d2f0 100644
--- a/sys/kern/vfs_sync.c
+++ b/sys/kern/vfs_sync.c
@@ -1,4 +1,4 @@
-/*       $OpenBSD: vfs_sync.c,v 1.63 2020/01/20 23:21:56 claudio Exp $  */
+/*       $OpenBSD: vfs_sync.c,v 1.64 2020/06/24 22:03:41 cheloha Exp $  */
 
 /*
  *  Portions of this code are:
@@ -142,7 +142,7 @@ syncer_thread(void *arg)
 	int s;
 
 	for (;;) {
-		starttime = time_second;
+		starttime = gettime();
 
 		/*
 		 * Push files whose dirty time has expired.
@@ -228,7 +228,7 @@ syncer_thread(void *arg)
 		 * matter as we are just trying to generally pace the
 		 * filesystem activity.
 		 */
-		if (time_second == starttime)
+		if (gettime() == starttime)
 			tsleep_nsec(&lbolt, PPAUSE, "syncer", INFSLP);
 	}
 }
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 44dcf3c117e..f195ac991dc 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vfs_syscalls.c,v 1.344 2020/03/19 13:55:20 anton Exp $	*/
+/*	$OpenBSD: vfs_syscalls.c,v 1.345 2020/06/24 22:03:42 cheloha Exp $	*/
 /*	$NetBSD: vfs_syscalls.c,v 1.71 1996/04/23 10:29:02 mycroft Exp $	*/
 
 /*
@@ -251,7 +251,7 @@ update:
 	 */
 	error = VFS_MOUNT(mp, fspath, args, &nd, p);
 	if (!error) {
-		mp->mnt_stat.f_ctime = time_second;
+		mp->mnt_stat.f_ctime = gettime();
 	}
 	if (mp->mnt_flag & MNT_UPDATE) {
 		vfs_unbusy(vp->v_mount);