svn commit: r295684 - in stable: 8/sys/kern 9/sys/kern

John Baldwin jhb at
Wed Feb 17 01:45:36 UTC 2016

Author: jhb
Date: Wed Feb 17 01:45:34 2016
New Revision: 295684

  MFC 295418,295419:
  Fix hangs or panics when misbehaved kernel threads return from their
  main function.
  Mark proc0 as a kernel process via the P_KTHREAD flag.
  All other kernel processes have this flag set and all threads in proc0
  (including thread0) have the similar TDP_KTHREAD flag set.
  Call kthread_exit() rather than kproc_exit() for a premature kthread exit.
  Kernel threads (and processes) are supposed to call kthread_exit() (or
  kproc_exit()) to terminate.  However, the kernel includes a fallback in
  fork_exit() to force a kthread exit if a kernel thread's "main" routine
  returns.  This fallback was added back when the kernel only had processes
  and was not updated to call kthread_exit() instead of kproc_exit() when
  threads were added to the kernel.
  This mistake was particularly exciting when the errant thread belonged to
  proc0.  Due to the missing P_KTHREAD flag the fallback did not kick in
  and instead tried to return to userland via whatever garbage was in the
  trapframe.  With P_KTHREAD set it tried to terminate proc0 resulting in
  other amusements.
  PR:		204999

Directory Properties:
  stable/8/sys/   (props changed)
  stable/8/sys/kern/   (props changed)

Changes in other areas also in this revision:
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/8/sys/kern/init_main.c
--- stable/8/sys/kern/init_main.c	Wed Feb 17 00:30:28 2016	(r295683)
+++ stable/8/sys/kern/init_main.c	Wed Feb 17 01:45:34 2016	(r295684)
@@ -451,7 +451,7 @@ proc0_init(void *dummy __unused)
 	session0.s_leader = p;
 	p->p_sysent = &null_sysvec;
-	p->p_flag = P_SYSTEM | P_INMEM;
+	p->p_flag = P_SYSTEM | P_INMEM | P_KTHREAD;
 	p->p_state = PRS_NORMAL;
 	knlist_init_mtx(&p->p_klist, &p->p_mtx);

Modified: stable/8/sys/kern/kern_fork.c
--- stable/8/sys/kern/kern_fork.c	Wed Feb 17 00:30:28 2016	(r295683)
+++ stable/8/sys/kern/kern_fork.c	Wed Feb 17 01:45:34 2016	(r295684)
@@ -878,7 +878,7 @@ fork_exit(callout, arg, frame)
 	if (p->p_flag & P_KTHREAD) {
 		printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
 		    td->td_name, p->p_pid);
-		kproc_exit(0);
+		kthread_exit();
 	mtx_assert(&Giant, MA_NOTOWNED);

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