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net: sock_def_readable() and friends RCU conversion

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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>
This commit is contained in:
Eric Dumazet 2010-04-29 11:01:49 +00:00 • committed by David S. Miller
parent 83d7eb2979
commit 4381548237
16 changed files with 181 additions and 114 deletions
Download patch file Download diff file Expand all files Collapse all files

47
net/socket.c
View file

@ -252,9 +252,14 @@ static struct inode *sock_alloc_inode(struct super_block *sb)
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 @@ static struct inode *sock_alloc_inode(struct super_block *sb)
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 @@ void sock_release(struct socket *sock)
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 @@ static int sock_fasync(int fd, struct file *filp, int on)
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 @@ static int sock_fasync(int fd, struct file *filp, int on)
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 @@ int sock_wake_async(struct socket *sock, int how, int band)
/* 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;
}