Clean up breakage in inferior() I introduced in 1.92 of kern_proc.c:

- Restore inferior() to being iterative rather than recursive.
- Assert that the proctree_lock is held in inferior() and change the one
  caller to get a shared lock of it.  This also ensures that we hold the
  lock after performing the check so the check can't be made invalid out
  from under us after the check but before we act on it.

Requested by:	bde

1 files changed, 3 insertions, 0 deletions

diff --git a/sys/kern/kern_prot.c b/sys/kern/kern_prot.c
index 5ffeeb7..9378d48 100644
--- a/sys/kern/kern_prot.c
+++ b/sys/kern/kern_prot.c
@@ -55,6 +55,7 @@
 #include <sys/lock.h>
 #include <sys/mutex.h>
 #include <sys/proc.h>
+#include <sys/sx.h>
 #include <sys/sysproto.h>
 #include <sys/malloc.h>
 #include <sys/pioctl.h>
@@ -443,6 +444,7 @@ setpgid(td, uap)
 
 	mtx_lock(&Giant);
 
+	sx_slock(&proctree_lock);
 	if (uap->pid != 0 && uap->pid != curp->p_pid) {
 		if ((targp = pfind(uap->pid)) == NULL || !inferior(targp)) {
 			if (targp)
@@ -488,6 +490,7 @@ setpgid(td, uap)
 	PROC_UNLOCK(targp);
 	error = enterpgrp(targp, uap->pgid, 0);
 done2:
+	sx_sunlock(&proctree_lock);
 	mtx_unlock(&Giant);
 	return (error);
 }