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net: sk_msg: Simplify sk_psock initialization

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Initializing psock->sk_proto and other saved callbacks is only
done in sk_psock_update_proto, after sk_psock_init has returned.
The logic for this is difficult to follow, and needlessly complex.

Instead, initialize psock->sk_proto whenever we allocate a new
psock. Additionally, assert the following invariants:

* The SK has no ULP: ULP does it's own finagling of sk->sk_prot
* sk_user_data is unused: we need it to store sk_psock

Protect our access to sk_user_data with sk_callback_lock, which
is what other users like reuseport arrays, etc. do.

The result is that an sk_psock is always fully initialized, and
that psock->sk_proto is always the "original" struct proto.
The latter allows us to use psock->sk_proto when initializing
IPv6 TCP / UDP callbacks for sockmap.

Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200821102948.21918-2-lmb@cloudflare.com
This commit is contained in:
Lorenz Bauer
2020-08-21 11:29:43 +01:00
committed by Alexei Starovoitov
parent dca5612f8e
commit 7b219da43f
5 changed files with 41 additions and 46 deletions
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17
include/linux/skmsg.h
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@@ -340,23 +340,6 @@ static inline void sk_psock_update_proto(struct sock *sk,
struct sk_psock *psock,
struct proto *ops)
{
/* Initialize saved callbacks and original proto only once, since this
* function may be called multiple times for a psock, e.g. when
* psock->progs.msg_parser is updated.
*
* Since we've not installed the new proto, psock is not yet in use and
* we can initialize it without synchronization.
*/
if (!psock->sk_proto) {
struct proto *orig = READ_ONCE(sk->sk_prot);
psock->saved_unhash = orig->unhash;
psock->saved_close = orig->close;
psock->saved_write_space = sk->sk_write_space;
psock->sk_proto = orig;
}
/* Pairs with lockless read in sk_clone_lock() */
WRITE_ONCE(sk->sk_prot, ops);
}