From: Peter Zijlstra <peterz@infradead.org>
To: Jason Baron <jbaron@akamai.com>
Cc: davem@davemloft.net, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, minipli@googlemail.com,
normalperson@yhbt.net, eric.dumazet@gmail.com,
rweikusat@mobileactivedefense.com, viro@zeniv.linux.org.uk,
davidel@xmailserver.org, dave@stgolabs.net, olivier@mauras.ch,
pageexec@freemail.hu, torvalds@linux-foundation.org
Subject: Re: [PATCH v2 3/3] af_unix: optimize the unix_dgram_recvmsg()
Date: Mon, 5 Oct 2015 09:41:51 +0200 [thread overview]
Message-ID: <20151005074151.GD2903@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <ba2b4c5c1d6fd3d99cd4b1286edace56c0f84a0d.1443817522.git.jbaron@akamai.com>
On Fri, Oct 02, 2015 at 08:44:02PM +0000, Jason Baron wrote:
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index f789423..b8ed1bc 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1079,6 +1079,9 @@ static long unix_wait_for_peer(struct sock *other, long timeo)
>
> prepare_to_wait_exclusive(&u->peer_wait, &wait, TASK_INTERRUPTIBLE);
>
> + set_bit(UNIX_NOSPACE, &u->flags);
> + /* pairs with mb in unix_dgram_recv */
> + smp_mb__after_atomic();
> sched = !sock_flag(other, SOCK_DEAD) &&
> !(other->sk_shutdown & RCV_SHUTDOWN) &&
> unix_recvq_full(other);
> @@ -1623,17 +1626,22 @@ restart:
>
> if (unix_peer(other) != sk && unix_recvq_full(other)) {
> if (!timeo) {
> + set_bit(UNIX_NOSPACE, &unix_sk(other)->flags);
> + /* pairs with mb in unix_dgram_recv */
> + smp_mb__after_atomic();
> + if (unix_recvq_full(other)) {
> + err = -EAGAIN;
> + goto out_unlock;
> + }
> + } else {
> @@ -1939,8 +1947,14 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
> goto out_unlock;
> }
>
> + /* pairs with unix_dgram_poll() and wait_for_peer() */
> + smp_mb();
> + if (test_bit(UNIX_NOSPACE, &u->flags)) {
> + clear_bit(UNIX_NOSPACE, &u->flags);
> + wake_up_interruptible_sync_poll(&u->peer_wait,
> + POLLOUT | POLLWRNORM |
> + POLLWRBAND);
> + }
>
> if (msg->msg_name)
> unix_copy_addr(msg, skb->sk);
> @@ -2468,20 +2493,19 @@ static unsigned int unix_dgram_poll(struct file *file, struct socket *sock,
> if (!(poll_requested_events(wait) & (POLLWRBAND|POLLWRNORM|POLLOUT)))
> return mask;
>
> other = unix_peer_get(sk);
> + if (unix_dgram_writable(sk, other)) {
> mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
> + } else {
> set_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
> + set_bit(UNIX_NOSPACE, &unix_sk(other)->flags);
> + /* pairs with mb in unix_dgram_recv */
> + smp_mb__after_atomic();
> + if (unix_dgram_writable(sk, other))
> + mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
> + }
> + if (other)
> + sock_put(other);
>
> return mask;
> }
So I must object to these barrier comments; stating which other barrier
they pair with is indeed good and required, but its not sufficient.
A barrier comment should also explain the data ordering -- the most
important part.
As it stands its not clear to me these barriers are required at all, but
this is not code I understand so I might well miss something obvious.
next prev parent reply other threads:[~2015-10-05 7:41 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-02 20:43 [PATCH v2 0/3] af_unix: fix use-after-free Jason Baron
2015-10-02 20:43 ` [PATCH v2 1/3] unix: fix use-after-free in unix_dgram_poll() Jason Baron
2015-10-03 5:46 ` Mathias Krause
2015-10-03 17:02 ` Rainer Weikusat
2015-10-04 17:41 ` Rainer Weikusat
2015-10-05 16:31 ` Rainer Weikusat
2015-10-05 16:54 ` Eric Dumazet
2015-10-05 17:20 ` Rainer Weikusat
2015-10-05 17:55 ` Jason Baron
2015-10-12 20:41 ` Rainer Weikusat
2015-10-14 3:44 ` Jason Baron
2015-10-14 17:47 ` Rainer Weikusat
2015-10-15 2:54 ` Jason Baron
2015-10-18 20:58 ` Rainer Weikusat
2015-10-19 15:07 ` Jason Baron
2015-10-20 22:29 ` Rainer Weikusat
2015-10-21 17:34 ` Rainer Weikusat
2015-10-28 16:46 ` [RFC] " Rainer Weikusat
2015-10-28 17:57 ` Jason Baron
2015-10-29 14:23 ` Rainer Weikusat
2015-10-30 20:52 ` [RFC] unix: fix use-after-free in unix_dgram_poll()/ 4.2.5 Rainer Weikusat
[not found] ` <57d2f5b6aae251957bff7a1a52b8bf2c@core-hosting.net>
2015-11-02 21:55 ` Rainer Weikusat
2015-10-02 20:43 ` [PATCH v2 2/3] af_unix: Convert gc_flags to flags Jason Baron
2015-10-02 20:44 ` [PATCH v2 3/3] af_unix: optimize the unix_dgram_recvmsg() Jason Baron
2015-10-05 7:41 ` Peter Zijlstra [this message]
2015-10-05 17:13 ` Jason Baron
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