socket poll related cleanups v2

socket poll related cleanups v2

[Christoph Hellwig]

Eric, Paul,

can you please look over the patch below?  The RCU annotations here don't
make any sense as we never RCU access through the annotated pointer (
we do access the underlying object through RCU and thus need to RCU free,
but that is a different story).  Dave doesn't seem to be convinced,
though.

[PATCH] net: remove bogus RCU annotations on socket.wq

[Christoph Hellwig]

We never use RCU protection for it, just a lot of cargo-cult
rcu_deference_protects calls.

Note that we do keep the kfree_rcu call for it, as the references through
struct sock are RCU protected and thus might require a grace period before
freeing.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/net.h |  2 +-
 include/net/sock.h  |  2 +-
 net/socket.c        | 10 ++++------
 3 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/include/linux/net.h b/include/linux/net.h
index 6554d3ba4396..e0930678c8bf 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -114,7 +114,7 @@ struct socket {
 
 	unsigned long		flags;
 
-	struct socket_wq __rcu	*wq;
+	struct socket_wq	*wq;
 
 	struct file		*file;
 	struct sock		*sk;
diff --git a/include/net/sock.h b/include/net/sock.h
index 7927541101a8..9b6011912691 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1725,7 +1725,7 @@ static inline void sock_graft(struct sock *sk, struct socket *parent)
 {
 	WARN_ON(parent->sk);
 	write_lock_bh(&sk->sk_callback_lock);
-	sk->sk_wq = parent->wq;
+	rcu_assign_pointer(sk->sk_wq, parent->wq);
 	parent->sk = sk;
 	sk_set_socket(sk, parent);
 	sk->sk_uid = SOCK_INODE(parent)->i_uid;
diff --git a/net/socket.c b/net/socket.c
index 5b7df6695f4f..475247e347ae 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -251,7 +251,7 @@ static struct inode *sock_alloc_inode(struct super_block *sb)
 	init_waitqueue_head(&wq->wait);
 	wq->fasync_list = NULL;
 	wq->flags = 0;
-	RCU_INIT_POINTER(ei->socket.wq, wq);
+	ei->socket.wq = wq;
 
 	ei->socket.state = SS_UNCONNECTED;
 	ei->socket.flags = 0;
@@ -265,11 +265,9 @@ static struct inode *sock_alloc_inode(struct super_block *sb)
 static void sock_destroy_inode(struct inode *inode)
 {
 	struct socket_alloc *ei;
-	struct socket_wq *wq;
 
 	ei = container_of(inode, struct socket_alloc, vfs_inode);
-	wq = rcu_dereference_protected(ei->socket.wq, 1);
-	kfree_rcu(wq, rcu);
+	kfree_rcu(ei->socket.wq, rcu);
 	kmem_cache_free(sock_inode_cachep, ei);
 }
 
@@ -603,7 +601,7 @@ static void __sock_release(struct socket *sock, struct inode *inode)
 		module_put(owner);
 	}
 
-	if (rcu_dereference_protected(sock->wq, 1)->fasync_list)
+	if (sock->wq->fasync_list)
 		pr_err("%s: fasync list not empty!\n", __func__);
 
 	if (!sock->file) {
@@ -1181,7 +1179,7 @@ static int sock_fasync(int fd, struct file *filp, int on)
 		return -EINVAL;
 
 	lock_sock(sk);
-	wq = rcu_dereference_protected(sock->wq, lockdep_sock_is_held(sk));
+	wq = sock->wq;
 	fasync_helper(fd, filp, on, &wq->fasync_list);
 
 	if (!wq->fasync_list)
-- 
2.18.0

Re: [PATCH] net: remove bogus RCU annotations on socket.wq

[Eric Dumazet]

On 07/30/2018 12:45 AM, Christoph Hellwig wrote:
> We never use RCU protection for it, just a lot of cargo-cult
> rcu_deference_protects calls.
> 
> Note that we do keep the kfree_rcu call for it, as the references through
> struct sock are RCU protected and thus might require a grace period before
> freeing.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Thanks.

Re: [PATCH] net: remove bogus RCU annotations on socket.wq

[Paul E. McKenney]

On Mon, Jul 30, 2018 at 03:23:06PM -0700, Eric Dumazet wrote:
> 
> 
> On 07/30/2018 12:45 AM, Christoph Hellwig wrote:
> > We never use RCU protection for it, just a lot of cargo-cult
> > rcu_deference_protects calls.
> > 
> > Note that we do keep the kfree_rcu call for it, as the references through
> > struct sock are RCU protected and thus might require a grace period before
> > freeing.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Reviewed-by: Eric Dumazet <edumazet@google.com>

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Re: [PATCH] net: remove bogus RCU annotations on socket.wq

[David Miller]

From: Christoph Hellwig <hch@lst.de>
Date: Mon, 30 Jul 2018 09:45:07 +0200

> We never use RCU protection for it, just a lot of cargo-cult
> rcu_deference_protects calls.
> 
> Note that we do keep the kfree_rcu call for it, as the references through
> struct sock are RCU protected and thus might require a grace period before
> freeing.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Applied to net-next, thanks.