[ltt-dev] [PATCH 3/7] urcu, defer_rcu: Avoid thread exit unexpected

[Mathieu Desnoyers]

Hi Lai,

I combined your patches 3 and 4, and enhanced them, including the
comments I sent for patch #2:


commit d7ff6cee89d7f8b4183b783d3d0a337b27d10bd2
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Date:   Thu Sep 29 13:28:04 2011 -0400

    urcu_defer: Use cancellation flag instead of pthread_cancel()
    
    - Provides better control over cancellation point location.
    - Set the futex to 0 before exiting the defer thread.
    
    This patch combines and enhances patches from Lai Jiangshan:
      urcu,defer_rcu: fix missing respond to a cancellation request
      urcu,defer_rcu: Avoid thread exit unexpected
    
    Reported-by: Lai Jiangshan <laijs at cn.fujitsu.com>
    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>

diff --git a/urcu-defer-impl.h b/urcu-defer-impl.h
index d1ab046..4211f7c 100644
--- a/urcu-defer-impl.h
+++ b/urcu-defer-impl.h
@@ -122,6 +122,7 @@ static pthread_mutex_t rcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
 static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 static int32_t defer_thread_futex;
+static int32_t defer_thread_stop;
 
 /*
  * Written to only by each individual deferer. Read by both the deferer and
@@ -148,7 +149,6 @@ static void mutex_lock_defer(pthread_mutex_t *mutex)
 			perror("Error in pthread mutex lock");
 			exit(-1);
 		}
-		pthread_testcancel();
 		poll(NULL,0,10);
 	}
 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
@@ -186,7 +186,13 @@ static unsigned long rcu_defer_num_callbacks(void)
 static void wait_defer(void)
 {
 	uatomic_dec(&defer_thread_futex);
-	cmm_smp_mb();	/* Write futex before read queue */
+	/* Write futex before read queue */
+	/* Write futex before read defer_thread_stop */
+	cmm_smp_mb();
+	if (_CMM_LOAD_SHARED(defer_thread_stop)) {
+		uatomic_set(&defer_thread_futex, 0);
+		pthread_exit(0);
+	}
 	if (rcu_defer_num_callbacks()) {
 		cmm_smp_mb();	/* Read queue before write futex */
 		/* Callbacks are queued, don't wait. */
@@ -359,7 +365,6 @@ void _defer_rcu(void (*fct)(void *p), void *p)
 void *thr_defer(void *args)
 {
 	for (;;) {
-		pthread_testcancel();
 		/*
 		 * "Be green". Don't wake up the CPU if there is no RCU work
 		 * to perform whatsoever. Aims at saving laptop battery life by
@@ -396,10 +401,17 @@ static void stop_defer_thread(void)
 	int ret;
 	void *tret;
 
-	pthread_cancel(tid_defer);
+	_CMM_STORE_SHARED(defer_thread_stop, 1);
+	/* Store defer_thread_stop before testing futex */
+	cmm_smp_mb();
 	wake_up_defer();
+
 	ret = pthread_join(tid_defer, &tret);
 	assert(!ret);
+
+	CMM_STORE_SHARED(defer_thread_stop, 0);
+	/* defer thread should always exit when futex value is 0 */
+	assert(uatomic_read(&defer_thread_futex) == 0);
 }
 
 int rcu_defer_register_thread(void)

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com