af_unix: fix EPOLLET regression for stream sockets
Commit 0884d7aa24 (AF_UNIX: Fix poll blocking problem when reading from
a stream socket) added a regression for epoll() in Edge Triggered mode
(EPOLLET)
Appropriate fix is to use skb_peek()/skb_unlink() instead of
skb_dequeue(), and only call skb_unlink() when skb is fully consumed.
This remove the need to requeue a partial skb into sk_receive_queue head
and the extra sk->sk_data_ready() calls that added the regression.
This is safe because once skb is given to sk_receive_queue, it is not
modified by a writer, and readers are serialized by u->readlock mutex.
This also reduce number of spinlock acquisition for small reads or
MSG_PEEK users so should improve overall performance.
Reported-by: Nick Mathewson <nickm@freehaven.net>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Alexey Moiseytsev <himeraster@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index aad8fb6..85d3bb7 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1918,7 +1918,7 @@
struct sk_buff *skb;
unix_state_lock(sk);
- skb = skb_dequeue(&sk->sk_receive_queue);
+ skb = skb_peek(&sk->sk_receive_queue);
if (skb == NULL) {
unix_sk(sk)->recursion_level = 0;
if (copied >= target)
@@ -1958,11 +1958,8 @@
if (check_creds) {
/* Never glue messages from different writers */
if ((UNIXCB(skb).pid != siocb->scm->pid) ||
- (UNIXCB(skb).cred != siocb->scm->cred)) {
- skb_queue_head(&sk->sk_receive_queue, skb);
- sk->sk_data_ready(sk, skb->len);
+ (UNIXCB(skb).cred != siocb->scm->cred))
break;
- }
} else {
/* Copy credentials */
scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).cred);
@@ -1977,8 +1974,6 @@
chunk = min_t(unsigned int, skb->len, size);
if (memcpy_toiovec(msg->msg_iov, skb->data, chunk)) {
- skb_queue_head(&sk->sk_receive_queue, skb);
- sk->sk_data_ready(sk, skb->len);
if (copied == 0)
copied = -EFAULT;
break;
@@ -1993,13 +1988,10 @@
if (UNIXCB(skb).fp)
unix_detach_fds(siocb->scm, skb);
- /* put the skb back if we didn't use it up.. */
- if (skb->len) {
- skb_queue_head(&sk->sk_receive_queue, skb);
- sk->sk_data_ready(sk, skb->len);
+ if (skb->len)
break;
- }
+ skb_unlink(skb, &sk->sk_receive_queue);
consume_skb(skb);
if (siocb->scm->fp)
@@ -2010,9 +2002,6 @@
if (UNIXCB(skb).fp)
siocb->scm->fp = scm_fp_dup(UNIXCB(skb).fp);
- /* put message back and return */
- skb_queue_head(&sk->sk_receive_queue, skb);
- sk->sk_data_ready(sk, skb->len);
break;
}
} while (size);