On Mon, 29 Jun 2009, Jiri Olsa wrote:

-static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
+static inline void __poll_wait(struct file *filp,
+				wait_queue_head_t *wait_address, poll_table *p)
+{
+	p->qproc(filp, wait_address, p);
+}
+
+static inline void poll_wait(struct file *filp,
+				wait_queue_head_t *wait_address, poll_table *p)
 {
 	if (p && wait_address)
-		p->qproc(filp, wait_address, p);
+		__poll_wait(filp, wait_address, p);
 }

+static inline void sock_poll_wait(struct file *filp, struct sock *sk,
+		poll_table *p)
+{
+	if (p && sk->sk_sleep) {
+		__poll_wait(filp, sk->sk_sleep, p);
+		/*
+		 * We need to be sure we are in sync with the
+		 * socket flags modification.
+		 *
+		 * This memory barrier is paired in the sk_has_sleeper.
+		*/
+		smp_mb();
+	}
+}

I think Oleg already said this, but you can use directly poll_wait() 
without adding another abstraction, and the compiler will drop the double 
check for you:

extern void foo(int, int, int);
extern void mb(void);

static inline void cfoo(int a, int b, int c) {
	if (b && c)
		foo(a, b, c);
}

void xxx(int a, int b, int c) {
	if (b && c) {
		cfoo(a, b, c);
		mb();
	}
}
-----
xxx:
	subq	$8, %rsp
	testl	%esi, %esi
	je	.L3
	testl	%edx, %edx
	je	.L3
	call	foo
	addq	$8, %rsp
	jmp	mb
.L3:
	addq	$8, %rsp
	ret



- Davide