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Commit 6f01fd6e authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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af_unix: fix EPOLLET regression for stream sockets 



Commit 0884d7aa (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: default avatarNick Mathewson <nickm@freehaven.net>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Cc: Alexey Moiseytsev <himeraster@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5b35e1e6

net/unix/af_unix.c

+4 −15
Original line number Diff line number Diff line
@@ -1918,7 +1918,7 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock, 
		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 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock, 
		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 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock, 


		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 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock, 
			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 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock, 
			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);