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>

1 files changed, 4 insertions, 4 deletions

diff --git a/net/phonet/pep.c b/net/phonet/pep.c
index e2a9576..af4d38b 100644
--- a/net/phonet/pep.c
+++ b/net/phonet/pep.c
@@ -664,12 +664,12 @@ static int pep_wait_connreq(struct sock *sk, int noblock)
 		if (signal_pending(tsk))
 			return sock_intr_errno(timeo);
 
-		prepare_to_wait_exclusive(&sk->sk_socket->wait, &wait,
+		prepare_to_wait_exclusive(sk_sleep(sk), &wait,
 						TASK_INTERRUPTIBLE);
 		release_sock(sk);
 		timeo = schedule_timeout(timeo);
 		lock_sock(sk);
-		finish_wait(&sk->sk_socket->wait, &wait);
+		finish_wait(sk_sleep(sk), &wait);
 	}
 
 	return 0;
@@ -910,10 +910,10 @@ disabled:
 			goto out;
 		}
 
-		prepare_to_wait(&sk->sk_socket->wait, &wait,
+		prepare_to_wait(sk_sleep(sk), &wait,
 				TASK_INTERRUPTIBLE);
 		done = sk_wait_event(sk, &timeo, atomic_read(&pn->tx_credits));
-		finish_wait(&sk->sk_socket->wait, &wait);
+		finish_wait(sk_sleep(sk), &wait);
 
 		if (sk->sk_state != TCP_ESTABLISHED)
 			goto disabled;