svn commit: r254578 - stable/9/sys/kern

[Bryan Venteicher]

Author: bryanv
Date: Tue Aug 20 19:13:13 2013
New Revision: 254578
URL: http://svnweb.freebsd.org/changeset/base/254578

Log:
  MFC r254457
    Do not use potentially stale thread in kthread_add()
  
    When an existing process is provided, the thread selected to use
    to initialize the new thread could have exited and be reaped.
    Acquire the proc lock earlier to ensure the thread remains valid.

Modified:
  stable/9/sys/kern/kern_kthread.c
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/9/sys/kern/kern_kthread.c
==============================================================================
--- stable/9/sys/kern/kern_kthread.c	Tue Aug 20 18:22:04 2013	(r254577)
+++ stable/9/sys/kern/kern_kthread.c	Tue Aug 20 19:13:13 2013	(r254578)
@@ -257,18 +257,17 @@ kthread_add(void (*func)(void *), void *
 		panic("kthread_add called too soon");
 
 	/* If no process supplied, put it on proc0 */
-	if (p == NULL) {
+	if (p == NULL)
 		p = &proc0;
-		oldtd = &thread0;
-	} else {
-		oldtd = FIRST_THREAD_IN_PROC(p);
-	}
 
 	/* Initialize our new td  */
 	newtd = thread_alloc(pages);
 	if (newtd == NULL)
 		return (ENOMEM);
 
+	PROC_LOCK(p);
+	oldtd = FIRST_THREAD_IN_PROC(p);
+
 	bzero(&newtd->td_startzero,
 	    __rangeof(struct thread, td_startzero, td_endzero));
 /* XXX check if we should zero. */
@@ -293,7 +292,6 @@ kthread_add(void (*func)(void *), void *
 	newtd->td_ucred = crhold(p->p_ucred);
 
 	/* this code almost the same as create_thread() in kern_thr.c */
-	PROC_LOCK(p);
 	p->p_flag |= P_HADTHREADS;
 	newtd->td_sigmask = oldtd->td_sigmask; /* XXX dubious */
 	thread_link(newtd, p);