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net: sock_def_readable() and friends RCU conversion

Browse source 
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 <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Eric Dumazet 2010-04-29 11:01:49 +00:00 • committed by David S. Miller
commit 4381548237
16 changed files with 181 additions and 114 deletions
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8
net/phonet/pep.c
View file

@ -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;

2
net/phonet/socket.c
View file

@ -265,7 +265,7 @@ static unsigned int pn_socket_poll(struct file *file, struct socket *sock,
struct pep_sock *pn = pep_sk(sk);
unsigned int mask = 0;
poll_wait(file, &sock->wait, wait);
poll_wait(file, sk_sleep(sk), wait);
switch (sk->sk_state) {
case TCP_LISTEN: