[PATCH net] af_unix: Avoid a wakeup if data has been not arrived

[PATCH net] af_unix: Avoid a wakeup if data has been not arrived

[Bin Zhong]

In the following scenarios, unnecessary wake-up may occur.
When a thread sends a piece of data and then immediately
calls recv to wait for the server's data, the server, upon
receiving this thread's data, calls back unix_write_space
to wake up this thread.

Therefore, add the filtering conditions of EPOLLIN and
EPOLLERR in the callback function of the waiting queue in
the unix_stream_data_wait function to reduce unnecessary
wake-ups.

Signed-off-by: Bin Zhong <zhongbin@bytedance.com>
---
 net/unix/af_unix.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index ac1f2bc18fc9..bd4e7beb02d5 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2500,6 +2500,14 @@ static int unix_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 	return recv_actor(sk, skb);
 }
 
+static int unix_stream_data_wake_function(wait_queue_entry_t *wait, unsigned int mode,
+					int sync, void *key)
+{
+	if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR)))
+		return 0;
+	return autoremove_wake_function(wait, mode, sync, key);
+}
+
 /*
  *	Sleep until more data has arrived. But check for races..
  */
@@ -2509,7 +2517,7 @@ static long unix_stream_data_wait(struct sock *sk, long timeo,
 {
 	unsigned int state = TASK_INTERRUPTIBLE | freezable * TASK_FREEZABLE;
 	struct sk_buff *tail;
-	DEFINE_WAIT(wait);
+	DEFINE_WAIT_FUNC(wait, unix_stream_data_wake_function);
 
 	unix_state_lock(sk);
 
-- 
2.25.1

Re: [PATCH net] af_unix: Avoid a wakeup if data has been not arrived

[Eric Dumazet]

On Wed, Jan 10, 2024 at 9:47 AM Bin Zhong <zhongbin@bytedance.com> wrote:
>
> In the following scenarios, unnecessary wake-up may occur.
> When a thread sends a piece of data and then immediately
> calls recv to wait for the server's data, the server, upon
> receiving this thread's data, calls back unix_write_space
> to wake up this thread.
>
> Therefore, add the filtering conditions of EPOLLIN and
> EPOLLERR in the callback function of the waiting queue in
> the unix_stream_data_wait function to reduce unnecessary
> wake-ups.

This is net-next material, and net-next is currently closed.

Also, I would rather re-use receiver_wake_function(), no need to copy paste it.

Thanks !