From 7ce60f6013d517e6a6cb29fd2670ff5a6acbfeaa Mon Sep 17 00:00:00 2001
From: David Xu <davidxu@FreeBSD.org>
Date: Tue, 10 Jul 2012 05:45:13 +0000
Subject: [PATCH] Always clear p_xthread if current thread no longer needs it,
 in theory, if debugger exited without calling ptrace(PT_DETACH), there is a
 time window that the p_xthread may be pointing to non-existing thread, in
 practical, this is not a problem because child process soon will be killed by
 parent process.

---
 sys/kern/kern_sig.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 52a0c405713..2685a8b1384 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -2436,9 +2436,10 @@ ptracestop(struct thread *td, int sig)
 		}
 stopme:
 		thread_suspend_switch(td);
-		if (!(p->p_flag & P_TRACED)) {
+		if (p->p_xthread == td)
+			p->p_xthread = NULL;
+		if (!(p->p_flag & P_TRACED))
 			break;
-		}
 		if (td->td_dbgflags & TDB_SUSPEND) {
 			if (p->p_flag & P_SINGLE_EXIT)
 				break;