kernel: remove global "randompid" toggle

Apparently, we used to created several kthreads before the kernel
random number generator was up and running.  A toggle, "randompid",
was needed to tell allocpid() whether it made sense to attempt to
allocate random PIDs.

However, these days we get e.g. arc4random(9) into a working state
before any kthreads are spawned, so the toggle is no longer needed.

Thread: https://marc.info/?l=openbsd-tech&m=165541052614453&w=2

Very nice historical context provided by miod@.

probably ok miod@ deraadt@

diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index bfc324c..a7413dc 100644 (file)
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: init_main.c,v 1.315 2022/02/22 01:15:01 guenther Exp $        */
+/*     $OpenBSD: init_main.c,v 1.316 2022/07/23 22:10:58 cheloha Exp $ */
 /*     $NetBSD: init_main.c,v 1.84.4.1 1996/06/02 09:08:06 mrg Exp $   */
 
 /*
@@ -431,8 +431,6 @@ main(void *framep)
                initprocess = initproc->p_p;
        }
 
-       randompid = 1;
-
        /*
         * Create any kernel threads whose creation was deferred because
         * initprocess had not yet been created.

diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 8b4b420..e5bdcc7 100644 (file)
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: kern_fork.c,v 1.240 2022/05/13 15:32:00 claudio Exp $ */
+/*     $OpenBSD: kern_fork.c,v 1.241 2022/07/23 22:10:58 cheloha Exp $ */
 /*     $NetBSD: kern_fork.c,v 1.29 1996/02/09 18:59:34 christos Exp $  */
 
 /*
@@ -67,7 +67,6 @@
 
 int    nprocesses = 1;         /* process 0 */
 int    nthreads = 1;           /* proc 0 */
-int    randompid;              /* when set to 1, pid's go random */
 struct forkstat forkstat;
 
 void fork_return(void *);
@@ -638,20 +637,22 @@ ispidtaken(pid_t pid)
 pid_t
 allocpid(void)
 {
-       static pid_t lastpid;
+       static int first = 1;
        pid_t pid;
 
-       if (!randompid) {
-               /* only used early on for system processes */
-               pid = ++lastpid;
-       } else {
-               /* Find an unused pid satisfying lastpid < pid <= PID_MAX */
-               do {
-                       pid = arc4random_uniform(PID_MAX - lastpid) + 1 +
-                           lastpid;
-               } while (ispidtaken(pid));
+       /* The first PID allocated is always 1. */
+       if (first) {
+               first = 0;
+               return 1;
        }
 
+       /*
+        * All subsequent PIDs are chosen randomly.  We need to
+        * find an unused PID in the range [2, PID_MAX].
+        */
+       do {
+               pid = 2 + arc4random_uniform(PID_MAX - 1);
+       } while (ispidtaken(pid));
        return pid;
 }
 

diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index ec2fd80..01fa10b 100644 (file)
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -1,4 +1,4 @@
-/*     $OpenBSD: proc.h,v 1.333 2022/07/05 15:06:16 visa Exp $ */
+/*     $OpenBSD: proc.h,v 1.334 2022/07/23 22:10:59 cheloha Exp $      */
 /*     $NetBSD: proc.h,v 1.44 1996/04/22 01:23:21 christos Exp $       */
 
 /*-
@@ -498,7 +498,6 @@ extern struct proc proc0;           /* Process slot for swapper. */
 extern struct process process0;                /* Process slot for kernel threads. */
 extern int nprocesses, maxprocess;     /* Cur and max number of processes. */
 extern int nthreads, maxthread;                /* Cur and max number of threads. */
-extern int randompid;                  /* fork() should create random pid's */
 
 LIST_HEAD(proclist, proc);
 LIST_HEAD(processlist, process);