1. Now that it's a thread's state is changed from within the kernel, where

   no userland locks are heald, the dead thread lock can no longer protect
   access to it. Therefore, instead of using an if (!dead)...else clause
   after walking the active threads list test the thread pointer before
   deciding not to walk the dead threads list. If the thread pointer is null
   it means it was not found in the active threads list and the dead threads
   list should be checked.

2. Do not free the stack of a thread that is not marked dead. This is the
   2nd and final part of eliminating the race to free a thread's stack.

MFC after: 3 days

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/libthr/thread/thr_exit.c b/lib/libthr/thread/thr_exit.c
index 6a4568788f32..f74b5e187775 100644
--- a/lib/libthr/thread/thr_exit.c
+++ b/lib/libthr/thread/thr_exit.c
@@ -195,7 +195,8 @@ deadlist_free_threads()
 	TAILQ_FOREACH_SAFE(ptd, &_dead_list, dle, ptdTemp) {
 		/* Don't destroy the initial thread or non-detached threads. */
 		if (ptd == _thread_initial ||
-		    (ptd->attr.flags & PTHREAD_DETACHED) == 0)
+		    (ptd->attr.flags & PTHREAD_DETACHED) == 0 ||
+		    !ptd->isdead)
 			continue;
 		TAILQ_REMOVE(&_dead_list, ptd, dle);
 		deadlist_free_onethread(ptd);