[lttng-dev] [PATCH] urcu: fix compat_futex_noasync()

[Lai Jiangshan]

This patch fix two critical problems:

1) compat_futex_cond is not bound to any @uaddr, it services all @uaddr,
   if you wakeup only one thread(pthread_cond_signal), the @uaddr of
   this waking thread and the @uaddr of the woken-up thread may be different.
   the the woken-up thread will very probably go to sleep again
   because his own condition is not true.

   *And* this waking thread(FUTEX_WAKE) wake up NOTHING.

2) If the caller want to wake up all waiting threads, he will use INT_MAX for @val.
   and 
		for (i = 0; i < INT_MAX; i++)
			pthread_cond_signal(&compat_futex_cond);
   becomes almost infinity loop.

Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
---
diff --git a/compat_futex.c b/compat_futex.c
index 04de596..bb928e6 100644
--- a/compat_futex.c
+++ b/compat_futex.c
@@ -43,7 +43,7 @@ static pthread_cond_t compat_futex_cond = PTHREAD_COND_INITIALIZER;
 int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
 	const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
 {
-	int ret, i, gret = 0;
+	int ret, gret = 0;
 
 	/*
 	 * Check if NULL. Don't let users expect that they are taken into
@@ -67,8 +67,7 @@ int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
 		pthread_cond_wait(&compat_futex_cond, &compat_futex_lock);
 		break;
 	case FUTEX_WAKE:
-		for (i = 0; i < val; i++)
-			pthread_cond_signal(&compat_futex_cond);
+		pthread_cond_broadcast(&compat_futex_cond);
 		break;
 	default:
 		gret = -EINVAL;