Move the cleanup code that frees memory allocated for a dead thread from

the thread kernel into a garbage collector thread which is started when
the fisrt thread is created (other than the initial thread). This
removes the window of opportunity where a context switch will cause a
thread that has locked the malloc spinlock, to enter the thread kernel,
find there is a dead thread and try to free memory, therefore trying
to lock the malloc spinlock against itself.

The garbage collector thread acts just like any other thread, so
instead of having a spinlock to control accesses to the dead thread
list, it uses a mutex and a condition variable so that it can happily
wait to be signalled when a thread exists.

1 files changed, 10 insertions, 5 deletions

diff --git a/lib/libpthread/thread/thr_find_thread.c b/lib/libpthread/thread/thr_find_thread.c
index 99e3023..e4a59a0 100644
--- a/lib/libpthread/thread/thr_find_thread.c
+++ b/lib/libpthread/thread/thr_find_thread.c
@@ -76,8 +76,12 @@ _find_dead_thread(pthread_t pthread)
 		/* Invalid thread: */
 		return(EINVAL);
 
-	/* Lock the dead thread list: */
-	_lock_dead_thread_list();
+	/*
+	 * Lock the garbage collector mutex to ensure that the garbage
+	 * collector is not using the dead thread list.
+	 */
+	if (pthread_mutex_lock(&_gc_mutex) != 0)
+		PANIC("Cannot lock gc mutex");
 
 	/* Point to the first thread in the list: */
 	pthread1 = _thread_dead;
@@ -85,11 +89,12 @@ _find_dead_thread(pthread_t pthread)
 	/* Search for the thread to join to: */
 	while (pthread1 != NULL && pthread1 != pthread) {
 		/* Point to the next thread: */
-		pthread1 = pthread1->nxt;
+		pthread1 = pthread1->nxt_dead;
 	}
 
-	/* Unlock the dead thread list: */
-	_unlock_dead_thread_list();
+	/* Unlock the garbage collector mutex: */
+	if (pthread_mutex_unlock(&_gc_mutex) != 0)
+		PANIC("Cannot lock gc mutex");
 
 	/* Return zero if the thread exists: */
 	return ((pthread1 != NULL) ? 0:ESRCH);