gistfile1.txt

diff --git a/mono/metadata/sgen-os-posix.c b/mono/metadata/sgen-os-posix.c
index 5a1f53d..4005a3b 100644
--- a/mono/metadata/sgen-os-posix.c
+++ b/mono/metadata/sgen-os-posix.c
@@ -51,6 +51,7 @@ static MonoSemType suspend_ack_semaphore;
 static MonoSemType *suspend_ack_semaphore_ptr;
 
 static sigset_t suspend_signal_mask;
+static sigset_t suspend_ack_signal_mask;
 
 static void
 suspend_thread (SgenThreadInfo *info, void *context)
@@ -104,6 +105,14 @@ suspend_thread (SgenThreadInfo *info, void *context)
 		mono_gc_get_gc_callbacks ()->thread_suspend_func (info->runtime_data, context);
 
 	DEBUG (4, fprintf (gc_debug_file, "Posting suspend_ack_semaphore for suspend from %p %p\n", info, (gpointer)mono_native_thread_id_get ()));
+
+	/*
+	Block the restart signal. 
+	We need to block the restart signal while posting to the suspend_ack semaphore or we race to sigsuspend,
+	which might miss the signal and get stuck.
+	*/
+	pthread_sigmask (SIG_BLOCK, &suspend_ack_signal_mask, NULL);
+
 	/* notify the waiting thread */
 	MONO_SEM_POST (suspend_ack_semaphore_ptr);
 	info->stop_count = stop_count;
@@ -114,6 +123,9 @@ suspend_thread (SgenThreadInfo *info, void *context)
 		sigsuspend (&suspend_signal_mask);
 	} while (info->signal != restart_signal_num && info->doing_handshake);
 
+	/* Unblock the restart signal. */
+	pthread_sigmask (SIG_UNBLOCK, &suspend_ack_signal_mask, NULL);
+
 	DEBUG (4, fprintf (gc_debug_file, "Posting suspend_ack_semaphore for resume from %p %p\n", info, (gpointer)mono_native_thread_id_get ()));
 	/* notify the waiting thread */
 	MONO_SEM_POST (suspend_ack_semaphore_ptr);
@@ -145,6 +157,15 @@ restart_handler (int sig)
 	int old_errno = errno;
 
 	info = mono_thread_info_current ();
+	/*
+	If the thread info is null is means we're currently in the process of cleaning up,
+	the pthread destructor has already kicked in and it has explicitly invoked the suspend handler.
+	
+	This means this thread has been suspended, TLS is dead, so the only option we have is to
+	rely on pthread_self () and seatch over the thread list.
+	*/
+	if (!info)
+		info = mono_thread_info_lookup (pthread_self ());
 
 	/*
 	 * If a thread is dying there might be no thread info.  In
@@ -254,6 +275,10 @@ mono_sgen_os_init (void)
 
 	sigfillset (&suspend_signal_mask);
 	sigdelset (&suspend_signal_mask, restart_signal_num);
+
+	sigemptyset (&suspend_ack_signal_mask);
+	sigfillset (&suspend_signal_mask, restart_signal_num);
+	
 }
 
 int