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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

17
net/unix/af_unix.c
View file

@ -313,13 +313,16 @@ static inline int unix_writable(struct sock *sk)
static void unix_write_space(struct sock *sk)
{
read_lock(&sk->sk_callback_lock);
struct socket_wq *wq;
rcu_read_lock();
if (unix_writable(sk)) {
if (sk_has_sleeper(sk))
wake_up_interruptible_sync(sk_sleep(sk));
wq = rcu_dereference(sk->sk_wq);
if (wq_has_sleeper(wq))
wake_up_interruptible_sync(&wq->wait);
sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
}
read_unlock(&sk->sk_callback_lock);
rcu_read_unlock();
}
/* When dgram socket disconnects (or changes its peer), we clear its receive
@ -406,9 +409,7 @@ static int unix_release_sock(struct sock *sk, int embrion)
skpair->sk_err = ECONNRESET;
unix_state_unlock(skpair);
skpair->sk_state_change(skpair);
read_lock(&skpair->sk_callback_lock);
sk_wake_async(skpair, SOCK_WAKE_WAITD, POLL_HUP);
read_unlock(&skpair->sk_callback_lock);
}
sock_put(skpair); /* It may now die */
unix_peer(sk) = NULL;
@ -1142,7 +1143,7 @@ restart:
newsk->sk_peercred.pid = task_tgid_vnr(current);
current_euid_egid(&newsk->sk_peercred.uid, &newsk->sk_peercred.gid);
newu = unix_sk(newsk);
newsk->sk_sleep = &newu->peer_wait;
newsk->sk_wq = &newu->peer_wq;
otheru = unix_sk(other);
/* copy address information from listening to new sock*/
@ -1931,12 +1932,10 @@ static int unix_shutdown(struct socket *sock, int mode)
other->sk_shutdown |= peer_mode;
unix_state_unlock(other);
other->sk_state_change(other);
read_lock(&other->sk_callback_lock);
if (peer_mode == SHUTDOWN_MASK)
sk_wake_async(other, SOCK_WAKE_WAITD, POLL_HUP);
else if (peer_mode & RCV_SHUTDOWN)
sk_wake_async(other, SOCK_WAKE_WAITD, POLL_IN);
read_unlock(&other->sk_callback_lock);
}
if (other)
sock_put(other);