do umtx_wake at userland thread exit address, so that others userland

threads can wait for a thread to exit, and safely assume that the thread
has left userland and is no longer using its userland stack, this is
necessary for pthread_join when a thread is waiting for another thread
to exit which has user customized stack, after pthread_join returns,
the userland stack can be reused for other purposes, without this change,
the joiner thread has to spin at the address to ensure the thread is really
exited.

1 files changed, 5 insertions, 1 deletions

diff --git a/sys/kern/kern_thr.c b/sys/kern/kern_thr.c
index e6661e2..39817df 100644
--- a/sys/kern/kern_thr.c
+++ b/sys/kern/kern_thr.c
@@ -42,6 +42,8 @@ __FBSDID("$FreeBSD$");
 #include <sys/signalvar.h>
 #include <sys/ucontext.h>
 #include <sys/thr.h>
+#include <sys/umtx.h>
+#include <sys/limits.h>
 
 #include <machine/frame.h>
 
@@ -275,8 +277,10 @@ thr_exit(struct thread *td, struct thr_exit_args *uap)
 	p = td->td_proc;
 
 	/* Signal userland that it can free the stack. */
-	if ((void *)uap->state != NULL)
+	if ((void *)uap->state != NULL) {
 		suword((void *)uap->state, 1);
+		kern_umtx_wake(td, uap->state, INT_MAX);
+	}
 
 	PROC_LOCK(p);
 	sigqueue_flush(&td->td_sigqueue);