Fix some locking nits with the p_state field of struct proc:

- Hold the proc lock while changing the state from PRS_NEW to PRS_NORMAL
  in fork to honor the locking requirements.  While here, expand the scope
  of the PROC_LOCK() on the new process (p2) to avoid some LORs.  Previously
  the code was locking the new child process (p2) after it had locked the
  parent process (p1).  However, when locking two processes, the safe order
  is to lock the child first, then the parent.
- Fix various places that were checking p_state against PRS_NEW without
  having the process locked to use PROC_LOCK().  Every place was already
  locking the process, just after the PRS_NEW check.
- Remove or reduce the use of PROC_SLOCK() for places that were checking
  p_state against PRS_NEW.  The PROC_LOCK() alone is sufficient for reading
  the current state.
- Reorder fill_kinfo_proc() slightly so it only acquires PROC_SLOCK() once.

MFC after:	1 week

5 files changed, 18 insertions, 25 deletions

diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index bca83b5..a979368 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -2634,9 +2634,11 @@ sysctl_kern_file(SYSCTL_HANDLER_ARGS)
 	xf.xf_size = sizeof(xf);
 	sx_slock(&allproc_lock);
 	FOREACH_PROC_IN_SYSTEM(p) {
-		if (p->p_state == PRS_NEW)
-			continue;
 		PROC_LOCK(p);
+		if (p->p_state == PRS_NEW) {
+			PROC_UNLOCK(p);
+			continue;
+		}
 		if (p_cansee(req->td, p) != 0) {
 			PROC_UNLOCK(p);
 			continue;
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index a29dc17..ebd4e6d 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -630,12 +630,13 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
 	/*
 	 * Set the child start time and mark the process as being complete.
 	 */
+	PROC_LOCK(p2);
+	PROC_LOCK(p1);
 	microuptime(&p2->p_stats->p_start);
 	PROC_SLOCK(p2);
 	p2->p_state = PRS_NORMAL;
 	PROC_SUNLOCK(p2);
 
-	PROC_LOCK(p1);
 #ifdef KDTRACE_HOOKS
 	/*
 	 * Tell the DTrace fasttrap provider about the new process
@@ -643,11 +644,8 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
 	 * p_state is PRS_NORMAL since the fasttrap module will use pfind()
 	 * later on.
 	 */
-	if (dtrace_fasttrap_fork) {
-		PROC_LOCK(p2);
+	if (dtrace_fasttrap_fork)
 		dtrace_fasttrap_fork(p1, p2);
-		PROC_UNLOCK(p2);
-	}
 #endif
 	if ((p1->p_flag & (P_TRACED | P_FOLLOWFORK)) == (P_TRACED |
 	    P_FOLLOWFORK)) {
@@ -660,12 +658,11 @@ do_fork(struct thread *td, int flags, struct proc *p2, struct thread *td2,
 		 */
 		td->td_dbgflags |= TDB_FORK;
 		td->td_dbg_forked = p2->p_pid;
-		PROC_LOCK(p2);
 		td2->td_dbgflags |= TDB_STOPATFORK;
 		_PHOLD(p2);
 		p2_held = 1;
-		PROC_UNLOCK(p2);
 	}
+	PROC_UNLOCK(p2);
 	if ((flags & RFSTOPPED) == 0) {
 		/*
 		 * If RFSTOPPED not requested, make child runnable and
diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c
index e02b5b2..34cc570 100644
--- a/sys/kern/kern_proc.c
+++ b/sys/kern/kern_proc.c
@@ -291,11 +291,11 @@ pfind(pid)
 	sx_slock(&allproc_lock);
 	LIST_FOREACH(p, PIDHASH(pid), p_hash)
 		if (p->p_pid == pid) {
+			PROC_LOCK(p);
 			if (p->p_state == PRS_NEW) {
+				PROC_UNLOCK(p);
 				p = NULL;
-				break;
 			}
-			PROC_LOCK(p);
 			break;
 		}
 	sx_sunlock(&allproc_lock);
@@ -756,7 +756,6 @@ fill_kinfo_proc_only(struct proc *p, struct kinfo_proc *kp)
 		kp->ki_sigcatch = ps->ps_sigcatch;
 		mtx_unlock(&ps->ps_mtx);
 	}
-	PROC_SLOCK(p);
 	if (p->p_state != PRS_NEW &&
 	    p->p_state != PRS_ZOMBIE &&
 	    p->p_vmspace != NULL) {
@@ -782,12 +781,11 @@ fill_kinfo_proc_only(struct proc *p, struct kinfo_proc *kp)
 	kp->ki_swtime = (ticks - p->p_swtick) / hz;
 	kp->ki_pid = p->p_pid;
 	kp->ki_nice = p->p_nice;
-	rufetch(p, &kp->ki_rusage);
-	kp->ki_runtime = cputick2usec(p->p_rux.rux_runtime);
-	PROC_SUNLOCK(p);
 	kp->ki_start = p->p_stats->p_start;
 	timevaladd(&kp->ki_start, &boottime);
 	PROC_SLOCK(p);
+	rufetch(p, &kp->ki_rusage);
+	kp->ki_runtime = cputick2usec(p->p_rux.rux_runtime);
 	calcru(p, &kp->ki_rusage.ru_utime, &kp->ki_rusage.ru_stime);
 	PROC_SUNLOCK(p);
 	calccru(p, &kp->ki_childutime, &kp->ki_childstime);
@@ -1213,13 +1211,11 @@ sysctl_kern_proc(SYSCTL_HANDLER_ARGS)
 			/*
 			 * Skip embryonic processes.
 			 */
-			PROC_SLOCK(p);
+			PROC_LOCK(p);
 			if (p->p_state == PRS_NEW) {
-				PROC_SUNLOCK(p);
+				PROC_UNLOCK(p);
 				continue;
 			}
-			PROC_SUNLOCK(p);
-			PROC_LOCK(p);
 			KASSERT(p->p_ucred != NULL,
 			    ("process credential is NULL for non-NEW proc"));
 			/*
diff --git a/sys/kern/kern_resource.c b/sys/kern/kern_resource.c
index 5bc3da5..66b6e2d 100644
--- a/sys/kern/kern_resource.c
+++ b/sys/kern/kern_resource.c
@@ -142,11 +142,9 @@ getpriority(td, uap)
 			uap->who = td->td_ucred->cr_uid;
 		sx_slock(&allproc_lock);
 		FOREACH_PROC_IN_SYSTEM(p) {
-			/* Do not bother to check PRS_NEW processes */
-			if (p->p_state == PRS_NEW)
-				continue;
 			PROC_LOCK(p);
-			if (p_cansee(td, p) == 0 &&
+			if (p->p_state == PRS_NORMAL &&
+			    p_cansee(td, p) == 0 &&
 			    p->p_ucred->cr_uid == uap->who) {
 				if (p->p_nice < low)
 					low = p->p_nice;
diff --git a/sys/kern/kern_thread.c b/sys/kern/kern_thread.c
index 5ef9864..29bdaa2 100644
--- a/sys/kern/kern_thread.c
+++ b/sys/kern/kern_thread.c
@@ -981,7 +981,9 @@ tdfind(lwpid_t tid, pid_t pid)
 				td = NULL;
 				break;
 			}
+			PROC_LOCK(td->td_proc);
 			if (td->td_proc->p_state == PRS_NEW) {
+				PROC_UNLOCK(td->td_proc);
 				td = NULL;
 				break;
 			}
@@ -990,12 +992,10 @@ tdfind(lwpid_t tid, pid_t pid)
 					LIST_REMOVE(td, td_hash);
 					LIST_INSERT_HEAD(TIDHASH(td->td_tid),
 						td, td_hash);
-					PROC_LOCK(td->td_proc);
 					rw_wunlock(&tidhash_lock);
 					return (td);
 				}
 			}
-			PROC_LOCK(td->td_proc);
 			break;
 		}
 		run++;