net: sock_def_readable() and friends RCU conversion
sk_callback_lock rwlock actually protects sk->sk_sleep pointer, so we
need two atomic operations (and associated dirtying) per incoming
packet.
RCU conversion is pretty much needed :
1) Add a new structure, called "struct socket_wq" to hold all fields
that will need rcu_read_lock() protection (currently: a
wait_queue_head_t and a struct fasync_struct pointer).
[Future patch will add a list anchor for wakeup coalescing]
2) Attach one of such structure to each "struct socket" created in
sock_alloc_inode().
3) Respect RCU grace period when freeing a "struct socket_wq"
4) Change sk_sleep pointer in "struct sock" by sk_wq, pointer to "struct
socket_wq"
5) Change sk_sleep() function to use new sk->sk_wq instead of
sk->sk_sleep
6) Change sk_has_sleeper() to wq_has_sleeper() that must be used inside
a rcu_read_lock() section.
7) Change all sk_has_sleeper() callers to :
- Use rcu_read_lock() instead of read_lock(&sk->sk_callback_lock)
- Use wq_has_sleeper() to eventually wakeup tasks.
- Use rcu_read_unlock() instead of read_unlock(&sk->sk_callback_lock)
8) sock_wake_async() is modified to use rcu protection as well.
9) Exceptions :
macvtap, drivers/net/tun.c, af_unix use integrated "struct socket_wq"
instead of dynamically allocated ones. They dont need rcu freeing.
Some cleanups or followups are probably needed, (possible
sk_callback_lock conversion to a spinlock for example...).
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/socket.c b/net/socket.c
index cb7c1f6..dae8c6b 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -252,9 +252,14 @@
ei = kmem_cache_alloc(sock_inode_cachep, GFP_KERNEL);
if (!ei)
return NULL;
- init_waitqueue_head(&ei->socket.wait);
+ ei->socket.wq = kmalloc(sizeof(struct socket_wq), GFP_KERNEL);
+ if (!ei->socket.wq) {
+ kmem_cache_free(sock_inode_cachep, ei);
+ return NULL;
+ }
+ init_waitqueue_head(&ei->socket.wq->wait);
+ ei->socket.wq->fasync_list = NULL;
- ei->socket.fasync_list = NULL;
ei->socket.state = SS_UNCONNECTED;
ei->socket.flags = 0;
ei->socket.ops = NULL;
@@ -264,10 +269,21 @@
return &ei->vfs_inode;
}
+
+static void wq_free_rcu(struct rcu_head *head)
+{
+ struct socket_wq *wq = container_of(head, struct socket_wq, rcu);
+
+ kfree(wq);
+}
+
static void sock_destroy_inode(struct inode *inode)
{
- kmem_cache_free(sock_inode_cachep,
- container_of(inode, struct socket_alloc, vfs_inode));
+ struct socket_alloc *ei;
+
+ ei = container_of(inode, struct socket_alloc, vfs_inode);
+ call_rcu(&ei->socket.wq->rcu, wq_free_rcu);
+ kmem_cache_free(sock_inode_cachep, ei);
}
static void init_once(void *foo)
@@ -513,7 +529,7 @@
module_put(owner);
}
- if (sock->fasync_list)
+ if (sock->wq->fasync_list)
printk(KERN_ERR "sock_release: fasync list not empty!\n");
percpu_sub(sockets_in_use, 1);
@@ -1080,9 +1096,9 @@
lock_sock(sk);
- fasync_helper(fd, filp, on, &sock->fasync_list);
+ fasync_helper(fd, filp, on, &sock->wq->fasync_list);
- if (!sock->fasync_list)
+ if (!sock->wq->fasync_list)
sock_reset_flag(sk, SOCK_FASYNC);
else
sock_set_flag(sk, SOCK_FASYNC);
@@ -1091,12 +1107,20 @@
return 0;
}
-/* This function may be called only under socket lock or callback_lock */
+/* This function may be called only under socket lock or callback_lock or rcu_lock */
int sock_wake_async(struct socket *sock, int how, int band)
{
- if (!sock || !sock->fasync_list)
+ struct socket_wq *wq;
+
+ if (!sock)
return -1;
+ rcu_read_lock();
+ wq = rcu_dereference(sock->wq);
+ if (!wq || !wq->fasync_list) {
+ rcu_read_unlock();
+ return -1;
+ }
switch (how) {
case SOCK_WAKE_WAITD:
if (test_bit(SOCK_ASYNC_WAITDATA, &sock->flags))
@@ -1108,11 +1132,12 @@
/* fall through */
case SOCK_WAKE_IO:
call_kill:
- kill_fasync(&sock->fasync_list, SIGIO, band);
+ kill_fasync(&wq->fasync_list, SIGIO, band);
break;
case SOCK_WAKE_URG:
- kill_fasync(&sock->fasync_list, SIGURG, band);
+ kill_fasync(&wq->fasync_list, SIGURG, band);
}
+ rcu_read_unlock();
return 0;
}