svn commit: r295674 - stable/10/sys/kern

[John Baldwin]

Author: jhb
Date: Tue Feb 16 21:36:48 2016
New Revision: 295674
URL: https://svnweb.freebsd.org/changeset/base/295674

Log:
  MFC 295418,295419:
  Fix hangs or panics when misbehaved kernel threads return from their
  main function.
  
  295418:
  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.
  
  295419:
  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
  Approved by:	re (glebius)

Modified:
  stable/10/sys/kern/init_main.c
  stable/10/sys/kern/kern_fork.c
Directory Properties:
  stable/10/   (props changed)

Modified: stable/10/sys/kern/init_main.c
==============================================================================
--- stable/10/sys/kern/init_main.c	Tue Feb 16 21:30:55 2016	(r295673)
+++ stable/10/sys/kern/init_main.c	Tue Feb 16 21:36:48 2016	(r295674)
@@ -479,7 +479,7 @@ 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_flag2 = 0;
 	p->p_state = PRS_NORMAL;
 	knlist_init_mtx(&p->p_klist, &p->p_mtx);

Modified: stable/10/sys/kern/kern_fork.c
==============================================================================
--- stable/10/sys/kern/kern_fork.c	Tue Feb 16 21:30:55 2016	(r295673)
+++ stable/10/sys/kern/kern_fork.c	Tue Feb 16 21:36:48 2016	(r295674)
@@ -1033,7 +1033,7 @@ fork_exit(void (*callout)(void *, struct
 	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);